You can pretty much get any pet you want. Though i recommend Cunning pets for BGs, Ferocity pets for Dungeons and Tenacity pets for questing. I have a lvl 26 hunter who has A spider for BGs, a Young Mesa Buzzard for Dungeoning and a Bear for questing. If you want more info go to wow-petopia.com.
Well, if you plan to Solo a lot of stuff, I'd say go turtle. Then you can cycle Shell Shield with your other pet damage reduction ability... I don't play anymore, so I can't remember, but Turtle or Gorilla imo.