XP off instancing is pretty decent til TBC, then XP drastically drops from runs... I personally prefer to always level off questing, cause dungeon grinding is just such a bore. I do dungeons at least once though, for sake of getting the quests done and chance for some blues.
I have not leveled at low lvl's since MoP came out, but I know before that I always ran dungeons. Quested between queues if I was on a DPS char.
Noticed dungeon exp from 85+ is laughable though, so there goes my plans on leveling my healers through dungeons to 90..
Is the exp in lower lvl dungeons really that bad now ? I hope not, I prefer to zerg through dungeons when leveling.
Pick up mining and herbalism, then quest while queuing up for randoms and you'll fly. You'll only want to do each dungeon once for the quests but questing outside the dungeon while picking plants and mining will get your level up so hopefully you don't hit the same dungeon twice.
Plus always move on to a higher area as soon as you hit the minimal level.
Create RaF account, dual-box ... profit!
No heirlooms needed
I soloed all the dungeons 15-35 on my Mistweaver Monk, bosses giving monstrous exp, thrash aoeing crazy exp, quests, all items for me. Leveled 1-31 in 8 hours (1-12 took most of the time )
I tanked, DPSed and healed the dungeons 31-50. ( When there are no tanks queuing, i queue as one and then i either let some monk windwalker tank with me healing ( and other healer too ) or me just taking the damage, having some probs with aggro but was immortal.
The "fastest" way to level is extremely personal. What works for one person may not work for someone else. That said though, I found that this nifty little addon worked wonders for me. WoW Pro (http://wow-pro.com/) Its free, and at least worth a shot. Some of the quests in the order the addon has you do them in is... questionable at times. But, again, it's all about personal taste. Hope this helps.
"Do not only practice your art, but force yourself into its secrets, for it and knowledge can raise men to the divine." -- Ludwig Van Beethoven
I personally just gather and queue for dungeons. That way I usually always have some decent gear when I move into a new zone for herbs and ore.
It probably isn't the fastest way however. The only quests I really do are the Donovan quest line in Winterspring for the trinket. In BC Ill so some quests to get my ilevel up but again, its mostly dungeons and gathering.
questing, just do the first dungeon of the day (gives most exp, unless they've changed it..), try to quest asap: quest accepted, check map, go towards it, complete it. BAM! next.
Best way is to buy a new account and raf it. Battlechest cost only 5 euro anyway, so I think it's worth it