Hi,You don't pick classes, you draw a die from the bag and that determines your class.
After reading the rules, I was wondering if there's a better reason to be Human other than the only idea I had:
It's best to be human if you can't guarantee which class you'll get.
I mean a random class could suck, but if I were first player and choosing my class last, then I think I'd pick a human just so I don't paint myself into a corner with class selection.
The only other thing I could think of is there's an expansion that adds race specific things.
IMO the benefit of being human is that you have two less modifiers to keep track off. Also, since classes are random you don't have to worry about getting a class that just doesn't work with your race (though with classes being two sided that isn't too much of a worry)