Which class gives most new magical powers for 1 level dip

Question

Background: I have a bard, who is a bit lacking in low level spell selection, so I've been looking into multiclassing to get some more.

Stats (you can give +2 ASI for the benefit of multiclassing):

STR 11, DEX 17, CON 14, INT 9, WIS 14, CHA 20

So, Wizard is out.

For classes that pick subclass at level 1, subclass features count of course.

From what I have gathered from unofficial internet snippets, Tasha's Cauldron of Everything seems give some nice options (like 4 cantrips and 5 1st level spells?!). But I don't have that book myself to verify, and I may have missed other options, so the question:

What is the most different spells or spell-like powers a 1-level multiclass dip can give?

To clarify: I mean spells the character can actually have available, not the number they can choose from. I also realize now, that divine casters who pick spells every morning are their own category, not directly comparable. Still, for purposes of this Q, count the daily prepared spells.

Bard isn't option for me, so I'll include it as an example: 4 cantrips, 2 spells, 1 magical ability (Bardic Inspiration).

UA is ok, though I'd prefer official classes.

Answer 1

Variety: Let's do some Math.

We're looking for variety of 1st level spell choices gained from a single level dip in another class. This means that we can immediately rule out the half-caster classes, Ranger and Paladin, as they do not get their spellcasting features until 2nd level.

Let \$B\$ be the set of 1st level spells a Bard can choose from. Let \$C\$ be the set of 1st level spells available to some other full caster class. Our objective is to find which class offers the greatest number of spells not already available to the Bard. Time to Math.

We begin with the well know identity:

$$|B\cup C|=|B|+|C|-|B\cap C|$$

Where \$|B\cup C|\$ is the number of 1st level spells that are either bard or {class} spells, \$|B|\$ is the number of bard spells, \$|C|\$ is the number of {class} spells, and \$|B\cap C|\$ is the number of spells appearing on both lists. So we are looking for the number of \$C\$ spells that are not also bard spells, which is \$|C|-|B\cap C|\$. Doing some simple algebra on the above identity, we have:

$$|C|-|B\cap C|=|B\cup C|-|B|$$

I've done the math for us, counting \$|C|\$ and \$|B\cup C|\$ on DNDBeyond. Here are the results, as well as the calculation of the number of spells gained from a single level dip into the class:

Class	Spells	Class or Bard Spells	Net Gain from 1 level Dip
Bard	24	24	0
Artificer	18	35	11
Cleric	16+2	36+2	12+2
Druid	21	35	11
Sorcerer	27+2	41+2	17+2
Warlock	13+2	32+2	8+2
Wizard	42	50	26

The Cleric, Warlock, and Sorcerer, depending on choice of domain, patron, or origin, could have up to 2 additional spells. This has been notated in the table by the "+2" in those rows.

Volume: Preparation is King

We've discussed the variety of choices afforded the different caster classes, but what we're really looking for here is the volume of magical expressions at our disposal. For this purpose, classes which prepare spells outclass the rest by significant margin.

In particular, the Cleric, Druid, and Artificer select spells each day from their entire respective lists (but Artificer is not an option as it is a 13 INT prereq). Here is the Cleric's feature:

You prepare the list of cleric spells that are available for you to cast, choosing from the cleric spell list. When you do so, choose a number of cleric spells equal to your Wisdom modifier + your cleric level (minimum of one spell). The spells must be of a level for which you have spell slots.

As a druid or cleric, you can prepare each day a number of spells equal to your 1 plus your Wisdom modifier, and they are chosen from the entire spell list of that class. This means that choosing druid for a 1 level dip gets you access to 11 additional spells you did not have access to before, and cleric can get you up to 14 additional spells you did not have access to before.

The Cleric's and Druid's flexibility and number of available spells is unmatched by any other class. Despite the Sorcerer's greater variety, the Sorcerer can only learn two 1st level spells with a single level dip. Here's the table:

Class	Cantrips Known	New Daily Accessible 1st Level Spells
Cleric	3	12+2
Druid	2	11
Sorcerer	4	2
Warlock	2	2