If we're to think about 4 of the same class...
4 Cleric would be interesting. Early Act 1 would be kind of tough, but Act 2 would be a breeze with quad Spirit Guardian obliterating everything.
4 Assassins would be interesting. Try and nuke down as much as you can in the first round!
The 4 Cleric has some real potential. I can also see 4 Rogue and do one as an Arcane trickster to get more spell power.
