Originally Posted by
therealbowser
Uh... what? Why would you even assume that?
On topic, it's really not as complicated as you might thing. For the 20-60 experience, it's just a matter of playing any zone you like. With a few exceptions, they are all totally viable and I would recommend covering zones you need for achievements/loremaster. There are some special exceptions -- people claim that the 10-20 zones are designed for players without mounts and are faster for those that do. I believe this to be true. Likewise, there are a couple zones to avoid -- specifically, Arathi Highlands and Silithus, as neither were updated Cataclysm. Duskwallow Marsh has an unusually high amount of running around too compared to typical Cataclysm renovations, as well. There may be others, but I doubt they are significant.
For 60-80, TBH, TBC should be avoided. The quests are too spread out and you'll be doing a lot of running around. That said, again.. if you need loremaster you may as well clear out any zones you still need. Why not, right? WotLK will provide the better experience overall, however. So if you don't need/don't care about loremaster, just hit that area up instead. I'd avoid some of the later zones until you have epic flying (IE Storm Peaks), but otherwise, it's a great continent to level in and by far has the better stories.
80-90 is totally up to you. IMO, both Cataclysm and MoP have equally effective leveling. It's just a question of which you prefer playing. I will however add that you should avoid doing Cataclysm dungeons, they tend to be highly overtuned.
Then we fall into Draenor. Well... Draenor is broken as shit. I don't know how to appropriately deal with Draenor yet, but there are supposedly tricks to leveling faster here. I'll defer to someone else's wisdom... and in fact, would request some tips myself for this area.
Dungeon leveling, by the way, is totally viable now, especially if you have a group that can do efficient pulls and not go afk for between every group. If you wish, you can try specific queuing and hitting each dungeon independently for quests. Again, though, I suggest you avoid Cataclysm dungeons, and some of the quests for these dungeons are locked behind quest chains anyways.
I don't know of any super special tips for leveling through this content beyond this. I'm curious where this thread will lead however as I am learning a bit myself, here.