I'm assuming that you have the orbs and there aren't any other greater vaults left, otherwise you should obviously go do those areas.
Have you killed Casino shopkeeper? Ancient Karmic Wyrm? Mommy water dragon? All worth a good pile of XP.
Given that you have a wish though, emperor moloch is probably fastest way.
If you haven't done so, you can kill the balors on D:50 for a pile of XP.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.