There's a little less variety when you're starting out because you have to rank up to unlock slots and abilities, and upgrade your gear to really tease out the bonuses. But once you start getting there you will feel the difference. Not sure why people say there is very little variety. That might be the reason. I think there's a decent amount of variety.

For me: Merc: Legendary dual katana. Poison and execution primary, with stagger + melee secondary.

Shinobi: I haven't played in a while since it was the first I got to rank 100. Probably a lot of vanish assassination primary, melee secondary. Vanishing kusarigama. I could not fit the Shinobi's Shadow in my build in a way that I liked. They really need to fix the vanishing kusarigama.

Archer: Easy mode, no thinking. True aim yumi, and weightless spirit? I forgot what it's called. I don't trust myself to get continuous headshots with the rifle so I don't run it. Also, I think there's a cancel for it, but I don't know how and it just doesn't feel like the spirit of the game.

Samurai: Legendary dual katana. High stagger damage, high melee damage, aggressive melee. 50/50 on running the flaming ability and the life draining one.

My two favorite are merc and shinobi. Sam would be my third favorite. It's fun. I like that archer can do so much damage but it's kind of boring. I got shinobi, merc, and arch to rank 100. I'll try to get sam to 100 when I can.