That got to be one of the more recent ones, as I spend more time playing in those. Hard to make 1 choice.

It may be AB 11, I remember it had some server issues but enough oldies and fun talk to make it memorable. AB 14 was a good one for me too, and was featured by the Epic staff! This year's main course was to play the scripted levels with tons of people, which made it another memorable Bash.