Getting back on topic.
The best was with the girlfriend of a colleague of mine many, many years ago. She's a knockout. Her colleague happened to be my friend too. After the kiss, things were really messed up for me.
Friend/colleague was away overseas. His girlfriend wanted to go to a disco with a couple of other girl colleagues of mine (plus me of course). The other girls pulled out. Me and her went to disco alone. She didn't have a bra, which is considered "daring" in Malaysia for Malaysian girls. She showed me "pills" -- "Good stuff, Anthony". Told her drugs are bad. She went to toilet. Came back looking happy. We sat down for a little. Then she just grabbed me and kissed me. Initial reaction was one of shock (my friend/colleague's girl, man), quickly replaced by "going with the flow". I think the kiss lasted about a minute, but it felt really long then to me. After a while, I suggested we go to a hotel. She recoiled and expressed a shock look. I said, "To have coffee... only". We went. Then we took a cab (didn't have a car back then) back to my place after I asked if she wanted to. Back home, up to my room, watched some TV while we cuddled and snogged a bit. I didn't sleep the whole night ("my friend's girl is with me") but she knocked off (most probably due to the drugs). In the morning, we rolled around a bit, kissed and kissed and kissed before I tasted, um, "one of them". Things were leading to "it" but all the while my mind was going "My friend's girl... she's hot... friend's girl... she's hot..." over and over again. I stopped, got a cab for her and she went home.
The kiss at the disco wasn't the best because the one just before the cab arrived at my home, to take her back to her's, was the best. Because we knew it wouldn't work out between us as she knows I can't betray my friend.
Excuse some of the stuff above but I thought it was necessary to convey the reason behind why that last kiss was the best for me.