Weird as it seems, for me it is a tie between his eyes and his brain. I love a man who can talk to me intelligently. I don't think you can size up a man's ability to fuck or satisfy you on the first meet, but I know in just a minute of two if fucking might be the only thing a guy might be good at. If I talk to someone (on a bus, the bar, at a club etc) and he engages me in intelligent talk about something we find mutually interesting, I might sit for hours, and have a few drinks and just talk with the guy. During the talk, I can find out a lot about him - and if he interests me enough, I'm sure to find out all about his cock and bedroom prowess as the relationship ages - maybe even by the next morning. But if he's a dumb ass, just staring at my tits and showing off his bulge, I might sleep with him, but probably not.