Having recently had my perceptions of my two favourite celebrity women utterly ruined in the last week, my hero worship utterly shattered, this is pretty hard to answer.
The physical alone just doesn't do it. Sex is always better with someone you (at the very least) like and better still if you can have a joke and some fun with it. It isn't always enough to look great, I tend to find myself wondering if I would want to go out for a coffee/beer with the person before I consider whether or not I want them in bed.
Suppose that boring women with no strong individuality are a major turn off.
So I suppose with hindsight the bet I can say is that I would like to travel back in time a bit for the best sex I never had with my friend Siobhan (not her real name), she was interested but I played chivalrous ass and thought that while there was a chance for her dying r/ship I probably shouldn't sleep with her. Now I know that the r/ship in question was already dead in the water at the time and it didn't matter one iota what I did, I should have played along with the seduction. Hell, one kiss from her and I was ready to pass out on the floor - not sure I could have survived much more but it would have been fun trying.
And then the friction and we drifted apart, so I lost her friendship too.
So yeah, my mate Siobhan (not her real name).