17hours 38mins this way on my paladin, 18hours 17 minutes on my hunter. (Alliance)
1-12 elly forest
12-17 Westfall (Do the 15/15 defias quest, 15 bandanas, and gnoll quest)
17-24 Redridge
24-28 Duskwood
28-32 Wetlands (North the dark iron auests)
32-35/36 Arathi do the mercenary/pathstalker quest then the follow up with the falconcrest, and otto quest (and the orc one).
35/36-45 Dustwallow Marsh. Amazing exp only down side is some hordes kill the best quest npc who gives you the raptor/grim totem tauren quests and you gotta wait for respawn.
45-52 Searing gorge. Do all quests except the escort one, pillow one, and the light the towers one.
52-55/56 Burning steeps
56-58 Ungoro crater
58-65/68 Hellfire.
65-68 Zangermarsh.
68-75 Borean Tundra
75-77 Grizzly Hills (Daily pvp quests are nice there too)
77-78 Zuldrak or whatever it's called. The ragemane quests, or the champions call(depending if someone will help you.)
78-80 Stormpeak goblin quests leading to Sons of Hodir.
Leveling within 2 days and never traveled to an inn to get rested xp. (Paladin did not use heirlooms)
Hope this helps.