Alterac valley at 40+ is amazing exp with RAF. Aslong as you are actually grinding mobs in between. Depends on your server que times also.

As a new player you'll probably want to have all of the same class to learn with.
5 shaman is still pretty fun but you can be overrun very fast at lower levels without any resilliance or tremor totem.
5 mages might be pretty fun for a new player

really just start a couple of sets and see which one you like.