Multiclassing is a fun bit of powergaming. Its okay to not multiclass, but it’s a lot of fun to see what you can get. Your value in this list is dependent on your character’s build, goals, and your game world’s (and DM’s) rules.
These are ranked entirely by how I feel about them, and also in a general “how well does this apply for the average character?” outlook.
1. The Rogue
The king class of Multi-class. Weapon based fighters might get a Sneak Attack die, which is a bit tasty, but EVERYBODY gets expertise in 2 skills of their choice, and that’s a tasty morsel. And stick around for level 2, where you get to Dash/Disengage/Hide as a Bonus Action. And all you need to qualify is a decent number in the most useful stat in the game. And you get a skill when you MC into it.
2. The Cleric
This may be a surprise, but Cleric is my #2. A level of full caster is nice, even though the cantrips are horrible. Still, clerics can repick their spells over a rest, and the fact that they get their domain at level 1 means even a splash is super flexible. Need heavy armor proficiency? There’s a domain for that. Want to attack as a bonus action? Or blind people? Or react to damage with lightning? There’s a domain for that and more. And sticking around until 2nd level gives you your Channel Divinity, extra oomph and a Turn Undead.
The best domains for a splash?
3. The Fighter
The most flexible Multiclass, as Str or Dex qualifies you. A great multiclass if you use a weapon. Pick a fighting style, gain a minor Bonus Action heal, and pick up weapon and armor proficiencies when you MC in. Second level nets you Action Surge, because who DOESN’T want to get a second action?
4. The Warlock
Look, I assume you know this, but if you have a high CHA, you should come here first. A rechargeable spell slot, a bunch of good cantrips, including on of the supposed best in the game, and a Patron to grant you power. All at first level. At second, you get an Invocation, which can be really really good.
Hexblade if you’re into that, but I recommend the Genie (not the Noble genie, the newer one. Still UA, tho.)
5. The Monk
A splash of monk is harder to qualify for, as it takes Dex and Wis, but if you’ve got that, then this is a good MC. Level 1 nets you a FREE!* attack as a bonus action, and a new way to calculate AC if you have the body, I mean, stats for it. Second level gives you some “Technically not magic” powers and a boost to movement.
6. The Barbarian
You need Str and Con to take this, but if Str isn’t your attack stat, think twice. A lot of Barb stuff is based on Str. Rage is a cool abillity, but not if you cast spells. You also need a lot of Con/Dex to be better than Medium armor, but maybe you’ve got that? A second level give you Reckless Attack, amazing if you use Str Melee attacks, and Danger Sense, which is great for dodging fireballs.
7. The Druid
First level of druid is a slog, unless you were hoping for spells? The druid does have some unique spells and cantrips, but nothing that a Magic Intiate feat can’t patch. Second level is where the fun begins, as you pick up Wildshape, on of the best features in the game for Utility and Exploration. Moon makes you a tank, but your level might mean that a Dire Wolf is a single round of Temp HP. But being able to crawl into the king’s bedroom as a spider for that assassination? Priceless.
8. The Paladin
Another 1st level slog, and one that takes 2 stats to get in to. Lay on Hands is a useful tool though, and I have personally seen Divine Sense matter once. Maybe twice? Second Level gets spell casting, although their list isn’t great, a fighting style, and Divine Smite, which is probably why you MC’d Paladin.
9. The Wizard
With Int your stat here, there’s not much synergy between this and other classes. But what you get with wizards is OPTIONS. 6 spells to your spellbook, including the option for Find Familiar, a class feature the accidentally tried to cram into a spell. Ritual caster gives you some great ways to use your new spells. And at second, another 2 spells, Arcane Recovery to get a slot back, and an arcane tradition. I don’t know if there’s any worth splashing, tho.
10. The Bard
The Bard is a great class to play, but a bad splash. Cha is nice, but the features are meh. Bardic inspiration can be good, but until you have 5 levels bard and they recharge on a short rest, do you really want to use them? And bard spells are… okay? At second level, you get song of rest and jack of all trades, which is… something?
11. The Sorcerer
More cantrips aren’t bad, but is this Cha caster worth a level? you do get your bloodline, but there aren’t great options. Dragon, I guess, gives you a permanent Mage Armor, but I don’t think many of the abilities are worth doing. Font of Magic at level 2 is okay, but unless you have plans to abuse it, it’s probably just there.
12. The Ranger
A certain kind of campaign makes Ranger Splash amazing. And that’s because I built my hexcrawl system assuming Rangers should be good at it. And Favored enemy could be good, but I’ve rarely seen it happen. Second level gives a fighting style and magic, including Hunters Mark, on of the better 1st level spells.
I will also make a note that a previous UA had a list of class options, some of which drastically change The Ranger’s place on this list.
13. The Artificer
Not going to beat around the bush: The first level here is worthless, and the second isn’t much better. Artificer needs 3 levels to be good, which is beyond the scope of splash. Do your self a favor if you want this flavor, play it from 1 up.
14. The Blood Hunter
Look, I’ll be honest, I don’t understand this class. It’s a complicated design that I haven’t had to figure out. And it’s gone through a couple iterations so I’m just lost. If your DM allows it, it might be worth a look, but it’s not in my games, so it’s at the bottom of the list.