I would pick a class or two that sounds fun and try it out. I leveled a few classes in HW and am slowly working on some for SB. Some I leveled for a while and then quit deciding I didn't like that class.

You can get to lvl 10 on any class in about an hour which gives a feel for what the class is about.

Why have more than one class? Sometimes you get tired of your chosen job and it's nice to be able to switch.