I've had experience on a hunter, rogue, druid, and my main 29 is a mage, from these I've come to the conclusion that hunters are always the best k/d ratio if they're any good at being a hunter. It's literally impossible to lose unless you get triple teamed by good rogues, and even then sometimes you come out on top if you have game. I've never seen a solo ANY other class do that much destruction in 29s.
With a healer? That's just not fair, cus me, a lowly mage, can destroy anything with a healer. Although, what I will say is that any class, played well, can destroy anyone else.
But if you're deciding on which 29 to play, don't choose a mage. Highly, highly, highly, highly don't recommend it. Unless you have severe dedication to wasting long hours getting raped in hunter full games to come to your best possible gear/spec setup, don't bother. You'll just get raped by just about everything.