2-man quest stacking. i track my xp-per-hour using titan panel. i only play on rested xp:
120,000+ xp/hr: AoE grinding with my mage in HFP
100,000 - 110,000 xp/hr: quest stacking (use Jame's leveling guide)
100,000 - 150,000 xp/hr: quest stacking while in 2-person group (my priest & a friend's same-level paladin). 2player and 3player quests are easy to complete, too.
i'm holy because paladin judgements buff holy damage. otherwise, i'd be shadow.
Edit:
Instances are more fun, have nice loot, and are a nice break if you're bored with doing the same quests for the 3rd character. But... they are not good for fast leveling. The time spending forming and gathering a group, as well as wipes & afk's, make for a lot of /played time that isn't earning xp. Plus there aren't many quests to complete.
Edited, Feb 1st 2008 11:34am by ixidoria