Ranger solo is nice, but I like magic stuffs more, so if there's a tank, I would play wizard. He really does nice damage, if he doesn't need to dodge bullets and stuff.
The paladin is a teamplayer, tanks and heals the group, but solo he isn't easy to be honest.
I never really played as sorcerer, the auto-aim thingy(left arrow key, forgot the name of the spell) is really nice, but if he is out of mana he got a problem. Poisoning a group of 20+ enemies that shoot at you isn't easy at all, but that's why he got HP.