It would appear exp parties of groups of 6 or more fighting mobs +5 levels above them is the most efficient way to level up right now.

Find a good camp with mobs +5 levels up that has a lot of mobs with quick spawns. Have a ranged puller or 2 run out and get a mob, bring it back, tank it, go get the next one, bring it back tank them both, etc etc etc. Crazy chains, 800+ exp per mob per person in the group. I've heard of people at level 30 getting to level 35 in 2 hours doing this.

How about Some LFG features in the game so we can find people looking for EXP Parties.