All 4 are fine Warrior and Paladin are harder to get to 80 since they start at level 1. Dark knight starts at 30 and for some stupid reasons that go unexplained Gunbreaker starts at 60 so it’s the easiest to get into

Mostly depends what your into, Everyone loves warrior for the ridiculous Fell cleaves, Everyone loves Paladin for the support, Everyone loves Dark Knight for the aesthetic and cool skills, and Everyone loves Gunbreaker for explosions and the obligatory “I like FF8”
Crowd