Taken from Reddit.
http://www.reddit.com/r/Diablo/comments/tyz34/insane_azmodan_exp_15_quest_turn_ins_per_kill/
I seriously think this is going to get patched real soon, maybe even with tonights maintenance, but on the off chance that it doesn't, here's the best exp possible assuming you have a 60 that can solo hell Azmodan (though it works in all difficulties). My friend got a char from 1 to 36 in 1.5 hours doing this, and we only had 3 people running (4 makes it exponentially better) and another friend went from 46 to 60 in a couple hours, again this wasn't a perfect run either, we were rusty and messed up a few times.
When you kill Azmodan, you get the chance to click on his soul to put it in the black soulstone, this is a quest completion and gives you 80-100k on hell mode, depending on your level. In addition to this, you get another quest to go up to the tower to finish the act. This ALSO gives you the same amount of exp, 80-100k. By splitting games up based on the following explanation, which may not be that great..., you can get absolutely NUTS exp per azmodan kill.
So this is going to be long and somewhat complicated but here it goes.
Players: A B C and D
* 1. A B C and D kill Azmodan, B,C,D Leave before soul and each click resume game
* 2. A picks up soul in his current game, and turns in tower quest = 2 quest completions,
* 3. A joins Bs game, B picks up soul, leaves game, and then resumes game. A then finishes tower quest for Bs game.= 2 Quest completions
* 4. A then join Bs game again, A finishes tower quest there, = 1 more quest completion
* 5. A and B join Cs game, C finishes Soul, B and C leave Cs game and resume new games, A then finishes tower quest = 2 more quest completions
* 6. A joins Bs game, finishes tower quest = 1 more quest completion
* 7. A and B join Cs game, finish tower quest = 1 more quest completion
* 8. A B and C join Ds game, D clicks soul, B C and D leave game and resume game. A then finishes tower quest = 2 more quest completions
* 9. A joins Bs game, finishes Bs tower quest = 1 more quest completion
* 10. A and B join Cs game, finish tower quest = 1 more quest completion
* 11. A B and C join Ds game, Finish twoer quest = 1 more quest completion
A gets 14 completions
B gets 9 Completions
C gets 5 completions
D gets 2 completions
The most important thing is to split the games up before the soul each time, and then again for each tower quest. Never click on the first soul with multiple people in the game.