Very generally, what is the difference between an Eldritch Knight and a Sorcerer with a dip into Fighter?

Question

I'm starting a new character in a D&D 5th game soon. The only D&D I've played is before 2nd edition, plus one session playing a sorcerer in (IIRC) D&D 3.5.

We're starting at 3rd level, to somewhat reduce the likelihood of immediate death. It will likely be two players and the GM, so combat roles aren't going to be strictly divided. And besides, I'm more focused on roleplaying than on optimizing for combat. I don't expect the campaign to run long enough for more than a couple level-ups.

I'm hearing a lot about how spellcasting is different and even Wizards and Clerics no longer have to prepare spells every day. It sounds like the main differences between a Sorcerer and Wizard is the list of available spells, and a Wizard's needs a spell book. So I'm leaning toward playing a Sorcerer again.

I mentioned I was thinking of playing a Sorcerer again, with a level in Fighter to not to be quite as worthless in combat, but got a counter suggestion to look at Eldritch Knight as an alternative. This is a class that as far as I know didn't even exist when I played the one session of 3.5 years ago, so I know nothing about it. The name suggests, however, that it's a kind of fighter with the ability to cast spells as well.

I don't have access to the PHB or other rulebooks until the chargen session, and won't have time to read much even then.

I'm looking to get a jump-start on my character class choice, with a compare and contrast of sorcerer 2/Fighter 1 with Eldritch Knight. I'm not much concerned with optimization, but I also don't want to make a choice that's obviously bad and will get my PC killed in the first battle, either.

What are the general differences between these two choices at level 3 and a few levels after?

Answer 1

I'd like to begin by noting that multiclassing is a dangerous choice, especially for a new player. If you choose any single character class, the 5e rules will generally guide you to a reasonable character that is viable in combat. If you multiclass, it's possible that some of the levels you take will be "deadweight" levels which won't help you significantly in combat, and your function in combat will be that of a lower-level character.

In particular: you've told us that you'd like to play as a sorcerer. As a sorcerer, your function in combat will be to cast spells, and your fighter level will not make you any better at that. So, although your survivability as a multiclass character will be higher, your damage output will be that of a second-level character in a third-level party, and that's a significant drawback.

So the general advice we have for players of D&D 5e, especially for inexperienced players, is to not multiclass.

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Let's now talk about details.

• As a third-level sorcerer, you would have six spell slots, two of which would be second-level. Good second-level sorcerer spells include invisibility, misty step, scorching ray, and shatter -- your four spells known could include two of these. Your AC might be 15 with mage armor or 12 without. When not spellcasting, you'd probably use the fire bolt cantrip, which deals 5.5 damage on average.
• As a third-level eldritch knight, you would have only two spell slots. But you would have a good weapon attack, you would have heavy armor, and you could use Action Surge, once per short rest, to attack twice. You might have AC 18 and average ten damage per attack (two-handed sword), or you might have AC 20 and average 7.5 damage per attack (longsword).
• As a sorcerer2/fighter1, you would have three spell slots and they would all be first-level. When not spellcasting, you'd use the fire bolt cantrip for 5.5 damage. But your AC would be 17 without using a spell slot, and you'd have the fighter Second Wind feature for 6.5 bonus hit points on average.

I don't think multiclassing serves you well here.

Now: third level is an unusually bad level to give up to multiclass to fighter, because the sorcerer gains a lot from their third level -- they double their spell slots and unlock a new level of spells. But fourth level is unusually bad too, because the sorcerer gains a lot from that one -- they get +2 to Charisma, which grants +1 to-hit and to save DC. Fifth level is especially terrible because the sorcerer gets fireball then, which can alter the course of whole combats.

What I'm saying is: giving up a level of sorcerer will hurt you a lot.

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I'd like to idly note: if you did want to improve your AC, you might also consider multiclassing to cleric. Most of the cleric domains will grant you proficiency with heavy armor -- you wouldn't get that multiclassing to fighter. Cleric will also grant you spell slot progression, so a sorcerer2/cleric1 would have the full six spell slots including two second-level spell slots. It's almost worth it, except that cleric doesn't grant you progression in sorcerer spells known, so you'd still be a level behind in most of the ways that are important.

Answer 2

I'll start by offering a few things that might help you make your own judgement, and clear up some misconceptions you seem to have.

Check the Basic Rules

Although you don't have access to the PHB until it's already time to make the character, a significant portion of the relevant content is available for free in the Basic Rules. They are available in PDF form from the Wizards of the Coast website, or in a more interactive form on D&D Beyond. Either one should be able to help you plan things somewhat in advance, though the specifics of the Eldritch Knight are not included. I'll be linking to pages within the D&D Beyond version whenever I can for this answer.

Spell preparation is changed, but not much

You mention that you heard "Wizards and Clerics no longer have to prepare spells every day", but that is deceptive at best. Some classes don't need to prepare spells, but Wizards and Clerics definitely do. If a prepared caster wants the same spells prepared on consecutive days then they don't strictly require separate preparation, but that particular difference is unlikely to have mechanical consequences. In the sense of "Wizards need to decide in the morning what spells they will cast during the day", that's (mostly) still true.

Useless in combat?

You stated that your reason for not being just a Sorcerer is that you don't want to be "worthless in combat", but Sorcerers don't match that by my description. Sorcerers are certainly fragile, but can be very effective in combat if they avoid getting hit.

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What does a Sorcerer with 1 level in Fighter look like?

The biggest thing that a Sorcerer gets from the first Fighter level is enhanced durability. Sorcerers can't use any armor effectively on their own, while a single level in Fighter gives at least medium armor, and depending on some other choices could also give heavy armor, a shield, and/or a flat +1 AC bonus at all times. Single-class Sorcerers can use mage armor and similar spells to make up for the lack of armor, but a Fighter dip will usually give an even better result and leave the extra spell-slot for other spells.

The other feature you get is Second Wind, which heals 1d10 plus fighter level HP refreshing on a short rest. For a low-level character that can be pretty significant, but it drops off quickly if you don't take more Fighter levels.

Other than those added durability options, your character would basically end up as a normal Sorcerer. Cantrips will be more effective than weapons in most if not all situations, and the difference only gets more significant as you level up Sorcerer more. Sorcerer spell progression is slowed by the dip, but you would still be able to reach all spell levels and those spells would be just as potent as a single-class sorcerer.

A second level in Fighter would grant the powerful Action Surge ability to enable the Sorcerer to cast two spells in a single turn. Most of the other Fighter features wouldn't benefit a Sorcerer much, especially not without a much larger number of Fighter levels.

What does an Eldritch Knight look like?

The Sorcerer with a little Fighter ended up being mostly a more durable Sorcerer. An Eldritch Knight is closer to the opposite end, and is a lot like a normal Fighter with some magic options. An Eldritch Knight will always be far behind a Sorcerer in terms of casting powerful spells; Sorcerers get access to higher level spells much earlier, and go all the way to potent 9th level spells, while Eldritch Knights gain spell levels so slowly that they only reach 4th level spells. Those spells aren't bad, but end up a lot closer to a Fighter with a small Wizard dip rather than a Sorcerer with a small Fighter dip.

It's also worth noting that Eldritch Knights use the Wizard spell list, which is significantly different from the Sorcerer's. I haven't gone through the whole thing, but it seems like the Wizard list has a lot of extra utility/control spells.

Summary

Eldritch knight is "Fighter with some spells". Sorcerer with a small Fighter multiclass is "Sorcerer with some armor". Either one would probably be fine enough, though the Sorcerer basically won't ever use weapons; if you want the character to be fighting with weapons sometimes then a different option would be better.

Alternatives

A Druid might be closer to the combat role you wanted, though the character concept is very different. Druids can use some armor and more weapons than Sorcerers and have a bit more HP, so they could be about as durable as a Sorcerer/Fighter mix. Druids have full spellcasting progression like Sorcerers, so can reach 9th level spells, but they also have the Wild Shape feature that allows them to turn into a Beast during combat. The Wild Shape form has its own HP, AC, and attacks, so the Druid can be a reasonably effective melee combatant while transformed. This ends up as a "shifting role" character compared to the Sorcerer/Fighter and Eldritch Knight which each aren't very effective at the other's role.

If one of the other players owns the Xanathar's Guide to Everything supplement, the Hexblade Warlock might be even better. Warlocks have some significant differences from other spell casters, but a Hexblade Warlock with Pact of the Blade can be built as a very capable melee-range character with potent spellcasting, as opposed to Eldritch Knight having limited spellcasting options or Sorcerer being weak in melee. Non-Hexblade Warlocks can still take Pact of the Blade, but it would be much weaker.

Answer 3

At 3rd level, the Eldritch Knight is more powerful unless you expect to fight large groups of enemies

Hit points:
22 + 3*Con (EK) vs 18 + 3*con (S/F)
The eldritch knight will generally be able to take approximately 1 additional attack from enemies

Offensive power:
At this level, using action surge is approximately equal to a 1st level spell (15 - 20 average damage on your turn for 2 attacks; 13 - 21 average damage on your turn for a spell)
2 1st level spells per day, 3 Action Surges per day (EK)
4 1st level spells per day (S/F)
The EK has an advantage here as well, because Action Surge recharges on a short rest.
Careful use of area-of-effect damage can put the S/F in the lead here though, as the average damage calculations I used above are assuming 2 creatures hit.

Defensive power is equivalent at this point, as both can use the same armor and shield options.

The Eldritch Knight is a more powerful choice at 3rd level here, unless you expect to be fighting hordes of enemies (where area-of-effect attacks can become much more valuable).

At 5th level, the Eldritch Knight is the better choice for a front line combatant, while Sorcerer/Fighter is much better as a mid line combatant.

The hit points gap grows even more here, and most importantly a level 5 fighter unlocks Extra Attack (two attacks per turn instead of one), and will be a much better weapon user than the Sorcerer/Fighter.

The Sorcerer/Fighter gets access to Metamagic (slightly modify spells on the fly), and is able to use spells in combat much more effectively - doubling spell effectiveness with Twin Spell, or simply casting more spells with Quicken Spell.

At 6th level and beyond, the Sorcerer/Fighter has 3rd level spells and can affect larger portions of a battle than the Eldritch Knight.

The Sorcerer/Fighter will never be quite as comfortable or durable on a front line as the Eldritch Knight (and the Eldritch Knight is much better once each has spent all their spells), but the power of higher level spells make the S/F a much more dangerous character - particularly to groups of enemies.

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All that said, you may also consider a full sorcerer - magic users (while less powerful than fighters in direct combat) are not worthless in 5th edition combat the way they were in 3.5 edition. Sorcerers get ranged and melee magic attack that is approximately 3/4 power compared to a fighter's basic attack that they can always use - these are the cantrips like Firebolt and Shocking Grasp. A full sorcerer also reaches the more powerful magic sooner than a Fighter/Sorcerer multiclass.

You would end up more defensively vulnerable with this choice though - a 13 to 16 Armor class instead of 18 or 19.