So a friend and I were invited to join another group's campaign. They just started and hit level 2 last session. Their current group is a Druid, Cleric, and a Barbarian. My friend is looking to play a martial class, most likely Paladin. I'm leaning towards the remaining spellcasters but keep bouncing around which one to stick with. An INT-based one would seem to make the most sense stat-wise for the group, but I figured I'd reach out and see what y'all would recommend.

Cheers in advance!

I think a stealth based dexterity character would fill out the party better than an intelligence caster.  Presently, you already have two caster classes here, and both Druids and Clerics have a few ways to help out of combat.  Sure, none of them do those things quite as well ad a Wizard, and the party would certainly benefit from a Wizard, but they sort of have that role covered. 

What they don’t have covered is someone who can get in and out of a situation.  A rogue or ranger would fill a niche the party presently does not have.  A bard could as well if you want a full caster, since this group doesn’t have any primary charisma characters—especially if the bard goes into dexterity as the secondary stat and takes expertise in stealth. 

Granted, party balance is overrated. The most important thing is just not choosing a character that steps on anyone else’s toes so everyone gets a chance to shine. 

It doesn't really matter that much which you choose. Int skills may be in short supply, but it's not mandatory to have them, and you can also shore that hole up by taking the skills on a non-int caster.

You might look at artificer. Int based, can fill lots of roles, and gets a thieves tool proficiency.

Given what the party has and what you're hoping to accomplish (Filling "holes" in party makeup) I'd second the Bard.  They get expertise, Dex is a great stat for them to build after Cha and with Magical Secrets, they can grab a wanted spell that will help the party, choosing from the entire spellbook.  I am playing a Bard in a campaign my group is staring and there's only 3 of us.  Barbarian, Artificer and Me, the Bard.  In my case, I am going to be healer/support, so my spells are being chosen pretty carefully at the moment, but I am also serving as scout/Rogue when needed.  

Also, as noted, party "balance" doesn't matter as much in 5e, but having a lot of bases covered means you have more options for solving problems and encounters.  More options is almost always better.

Play what you want, and don't worry about what "makes sense". If you feel like you need to "fill holes" in the party makeup, you can always choose a background that provides a couple skills no one else has. Be a wizard if that's what's calling to you, but with the Criminal background if no one else can pick those locks

Eldritch knight is a good intelligence based half spell class. It’d also provide some great spells like haste, invisibility, etc.

Other than that, maybe a warlock would help. They’re a little squishy but with 3 healers you should be fine

Quote from Jhadzaan >>

So a friend and I were invited to join another group's campaign. They just started and hit level 2 last session. Their current group is a Druid, Cleric, and a Barbarian. My friend is looking to play a martial class, most likely Paladin. I'm leaning towards the remaining spellcasters but keep bouncing around which one to stick with. An INT-based one would seem to make the most sense stat-wise for the group, but I figured I'd reach out and see what y'all would recommend.

Cheers in advance!

 
Your group needs a skill monkey. I would’ve said Rogue, but you said you wanna play a spellcaster. Then I was gonna say Bard, but you said you want to play an Int caster for party balance, so ultimately I’ll say Artificer. It’s an Int caster skill monkey, and one of my favorite classes quite frankly. I think you’ll love it. You could still go with a Rogue and choose Arcane Trickster as the subclass, that would work too. It’s an Int caster skill monkey after all, and a really good one. But that really narrows your choice down to the one subclass, whereas with an Artificer you have several subclasses to choose from.

Quote from Jhadzaan >>

So a friend and I were invited to join another group's campaign. They just started and hit level 2 last session. Their current group is a Druid, Cleric, and a Barbarian. My friend is looking to play a martial class, most likely Paladin. I'm leaning towards the remaining spellcasters but keep bouncing around which one to stick with. An INT-based one would seem to make the most sense stat-wise for the group, but I figured I'd reach out and see what y'all would recommend.

Cheers in advance!

 Ok, so to figure this out, you have the following things:

1. A tank
2. A slightly less tanky support tank
3. A healer
4. A slightly less powerful healer.

Overall that doesn’t seem like good class mixture anyway in my opinion. I would probably play a damage focused spellcaster, because that is what the party lacks. I would recommend fiend warlock, because they can deal large amounts of damage, but only if the party takes short rest frequently. That might be unlikely tho, cuz the entire party is literally either a healer or a tank. So, if that isn’t the case, then I would personally be a wizard with the tough (constitution) and resilient feats, for survivability. This will supply a lot of high-damage spells, and you won’t be a glass cannon (as long as you have a 20 constitution), because of the tough feat.

It is 5e you can have a party of all the same class and it will still work, play what makes you happy.

+1 for the "just make sure you're not stepping on toes crowd".

You don't need to cover every aspect of the game, you just need to have enough capability to execute your strategy. You can adapt your strategy according to your party make-up.

What you don't want to do is be the same as someone else (NB: that doesn't mean the same class - an Evocation Wizard is a very different beast to a necromancer Wizard, while a Moon Druid can easily clash with a Path of the Totem Warrior Bear Barbarian). Why not? Because it gets frustrating and boring. If you're both built to be awesome at, say, thieving and general Sleight-of-Hand hijinks and not much else, every time an opportunity to snatch something comes up, you'll be arguing and only getting half of the opportunities to be the hero in the limelight. Pick different roles so you get your own niche.

So play what you want. Looking at that party make-up, I'd avoid being a tank or a healer. Both are very crowded niches in that party (three of them healers and, depending on subclass, all could be tanks).

That's a wide open field, my friend. I'd personally stay away from Wisdom builds since they already have two. So, a Dex (Rogue in particular) build would do well, possibly Arcane Trickster if you wanted to invest in Intelligence anyway. Or you could go archer, perhaps as a Fighter. Ranger is more generalist and leans into Wis, which is already covered by the Druid and Cleric.

You could go for an Int build, Artificer would get you somewhere similar to an Arcane Trickster or you could go full caster with a Wizard.

You could go Cha, you'd compete a little with the Paladin but it's not going to be major and will be nothing compared to the issues the three original party members will be facing. You'll barely notice. You could then go Warlock or Sorcerer (going Paladin might be a bit much).

You could go Monk, Bard or Ranger, but with two Wis builds already, you'd probably find that the skills are taken. It could easily still be fun, but it'll just be a little cosy with three of you there.

As you can see, my main counsel is to avoid making being a tank or healer part of your character's identity. There area couple of minor concerns beyond that, but nothing that you should allow to get in the way of playing a concept you're excited about.

And in an odd turn the Paladin player is now going Monk. Looks like Bard or Warlock now. Maybe Bard with a 1 level dip in Warlock or Sorcerer for armor/MAD/cantrips/etc depending on the subclass taken. Ah the options...:D