If you're a member, go to Nightmare, the room with 4 level 99 Nothings (yes, that's what they are called)

If you're a free player, go to Ice Storm Arena.

Sadly, I do not know a faster way to obtain EXP.  Except for ultra boss fights (which are dailies), the Awe-scended quests, and the Dragon of Time quests, quests just don't seem to give enough.  The grind for EXP is mind-numbingly boring.  Although if you wish to be at the top of the game, it is essential.  I'd advise you to remember your buffs and grind EXP during double EXP days.