Hmm.
Two things.
For a duo leveling team, warrior "can" be good, the class IS the best for tanking, even if not specced full prot. Cant heal worth a dog's hind end tho, so limits the massive pulls a druid/pally=lock combo can pull off.
Rogues have CC. thats about it. get 2-3 = lvl mobs on them.. and your gonna be doing CC as a lock. you cant heal, neither can he.....
Remeber an essential part of leveling is making sure you have good gears.
2 people, that want to level fast, do some instances (tho not as many as you can)
Loki, is kinda right about doing it with a BM hunter.. but it will suck until he gets the pet rage thing. And if Loki had read, you said anything BUT a hunter.
I still say a feral druid or a pally. nothing like a tanky pew pew that can heal.