I always did pretty well back in the day with a fury warrior (me) and a ret pally (guildy/friend). We tore through pretty much everything.
Actually, I tend to be pretty one dimensional and stick to a single class as my main. My friend, on the other hand, likes to alt hop and even do crazy things such as get a character to 90 then delete it to level one again. So, seeing as how we play together a lot, I've ended up running around/questing with pretty much every class he's played. From what I've found, we tend to do better when he's either on one of his plate DPS/tank classes or any class that can heal me.