Cure Light Wounds is on spell lists of:
Those guys can all use a Wand of Cure Light Wounds without rolling Use Magic Device even if they can't cast CLW normally yet, e.g. level 1 Paladins, who don't even have Caster Levels yet. The very fact that they have it on their spell list suffices.
Infernal Healing is on spell lists of:
- Summoners. If you are playing PFS, you have to play an Unchained Summoner, who is nerfed and whose spell list doesn't include Infernal Healing.
Since Infernal Healing has the [evil] descriptor, it is unavailable for Good Clerics, and Paladins may or may not have problems with it.
If you don't belong to any of those classes and don't cast from any of the above spell lists, the odds of meeting someone who does are a lot higher if you stick with Cure Light Wounds. On the other hand, if you can cast Infernal Healing, but not Cure Light Wounds, it might be a good idea to stick with the former. Also, if you can use the Wand of CLW but get dropped, it’s more likely that your potential savior will be able to use it than it is with Infernal Healing.
Gold per healing
One application of Cure Light Wounds costs 15 gp and heals 2 to 9 HP if cast from a Wand (5.5 HP on average). Infernal Healing always heals 10 HP per application and costs the same. On average, Infernal Healing is 82% more efficient.
Note that outside of PFS you can also craft a custom magic item that would cast CLW or Infernal Healing for you on a command word. The cost of this item would be 2,000 gp, of which you will only pay 1,000. Anyway, that's the cost of more than 2.5 level 1 wands. Usually, this won't be effective, but if you go through wand charges too quickly, it will.
Time to use
- Cure Light Wounds only requires a Standard action to use, and Infernal Healing has a casting time of 1 round.
- CLW is an Instantaneous spell, while Infernal Healing works over 10 rounds.
Overall, it takes 66 seconds (11 rounds) for one application of Infernal Healing to be cast upon and to end for one target. This makes Infernal Healing completely non-viable when time is limited. The more you level up, the more you have to wait to heal each time. For example, a level 6 Wizard with around 38 HP will have to wait for 42 rounds (4 minutes 12 seconds) to heal fully after being dropped to 0. The same task would require an average of 6.9 casts of CLW, or 7 rounds (1 minute 6 seconds).
On average, CLW heals 5.5 HP per round, and Infernal Healing heals pretty much 0.91 HP per round, making CLW around 6 times faster. If you start reapplying Infernal Healing the round before it is going to vanish, this number will come closer to 1 HP per round the more HP you heal, bringing the speed difference closer to 5.5 times.
Note that you can speed things up by using both spells if you need to heal a lot of HP. Not counting the first round when you cast Infernal Healing, you will cast Cure Light Wounds 9 times and then reapply Infernal Healing. Over those 10 rounds, you will heal an average or 5.5*9+10=59.5 HP instead of 55.5 HP with just Cure Light Wounds. Healing speed increases by about 7%, which may or may not matter for you, depending on the circumstances.
Also, you can apply Infernal Healing to many creatures one after another if you need to heal a lot of characters but are short on healers.
- Extremely early on, Cure Light Wounds can be used to damage certain Undead when there is no other way to hit them.
- Infernal Healing can be applied right before combat or at the beginning of combat. If an affected ally drops, they will be instantly healed for 1 HP and stabilized... granted they survive the damage. This situation is unlikely to actually happen in practice: if you have time to prepare for an encounter less than a minute before it begins, there are usually better things to cast.
- Cure Light Wounds cannot be used on creatures that get damaged by positive energy.
- If you often have to heal such characters, you can buy Inflict Light Wounds instead, which would work for them exactly as Cure Light Wounds doesfor normal characters.
- Infernal Healing doesn't heal damage caused by silver and good-aligned weapons, and by spells/effects with a [good] descriptor.
Both of those limitations should kick in pretty rarely, but when one spell doesn't work for some reason, it's very likely that you will want the other one very much.
As noted before, Infernal Healing is also an [evil] spell. Outside of PFS, if you use it consistently over a long time period, you might turn Evil yourself, at GM's discretion. This may or may not be a downside for you, and if you are already Evil, it is clearly not.
If your class has Cure Light Wounds on its spell list, but not Infernal Healing, definitely go with Cure Light Wounds first. If you buy Infernal Healing, the odds are that you will rarely get to use your Wand without UMD.
If you are a neutral Cleric or a Witch (or just use those spell lists), you might want to acquire a Wand of CLW and then a Wand of Infernal Healing, choosing the right advantage for the right situation. The same goes for evil Clerics (who are not legal in PFS). Note that Evil Clerics have no problems with casting Cure spells.
If you play in a rather stable group that has casters of both spells, you might want both wands. You will use Infernal Healing for its cost-effectiveness, and Cure Light Wounds to heal faster, or even combine them as noted before.
If you play in a stable group that can only cast Infernal Healing without UMD, buy Infernal Healing, but you still might want Cure Light Wounds for an emergency case and for healing faster once your UMD score improves.
If your stable group needs UMD for both spells... well, really make sure that you have someone, better at least two people with high UMD scores. PFS scenarios assume the players having some sort of healing available: I know that both from my own experience and from many PFS guides.
Which spell is better for you depends largely on your class and on your party composition.
Your mileage may vary greatly based upon the preferences of your local players. For example, if nobody plays Clerics, Witches, Magi, Wizards, Sorcerers, or Arcanists around your area, Infernal Healing is very unlikely to be of any use. If your party consists of 4 Wizards and you don't play with anybody else, using Cure Light Wounds will require UMD, but Infernal Healing never will.
A note on combat healing
It might be tempting to use one of the Wands in combat, but don't: it's going to be a negative game for you. Combat healing is almost never efficient in Pathfinder because usually you spend an action, but heal less than an enemy damages with one attack.
Barring an emergency (someone bleeding out), healing someone in combat can even do worse for them — someone who is down and out tends to be ignored by most enemies, but someone up with a couple HP is much more likely to get finished off in one hit.