Absolutely no doubt for me - Atomic Jam @ the Que Club - words cannot sum it all up, basically, my spiritual home, those were heavy nights and they will live forever in my now fragile head.
There are two very close runners up though:
HOG @ Subway City - An atmosphere that was totally unique in every way, I used to come out of there feeling dirty from the inside, yet elated, as if I had done something naughty and gotten away with it.
Raves in a clearing in the woods in wales, or anywhere else for that matter. This is the shit that got me into all of this in the first place, so it would be criminal to ignore the roots.