I've been playing WoW for quite some time now, and have had a chance to level quite a few characters (thanks, altaholism!). It's simply a fact that some classes and some specs are easier and/or funner to level than others: on one side of the spectrum, you've got your Holy Priests, Prot Warriors, and (any spec) Paladins; on the other side, there's Shadow Priests, Rogues, Hunters, etc. I think I'd have to say that overall, my most painless leveling experience has been my Priest, whom I leveled Shadow (until 1.10 came out, when I switched to a lolsmite build just for kicks), followed by my Rogues, Combat both.
I'm a big believer in having a separate leveling spec from your endgame spec. For me, it just makes the whole process much easier to maximize efficiency. Some players, though, advocate playing your endgame spec throughout, or at least from level 40 or so, in order to "get a feel" for it. What do you think, faithful readers? Leveling specs: the quick road to 60, or the quick road to being a 60 who has no idea what the heck they're doing? What was your best/worst leveling experience?
One final question: I'll be rolling a Draenei warrior in the expansion. How should I spec him for leveling (PvP not a real concern)? I'm thinking Fury, but I don't have a ton of warrior experience.