We were talking recently, just in general, what we liked about sex. It wasn't a "tell me your deep dark secrets" kind of thing. It was things like "I like being on top more than missionary", "do you like doggie style more than on top" etc.
She stated that her favorite position is her on top (Cowgirl), with me using my fingers or some vibrating mechanism. The combination of penetration and clitorial stimulation really brings it all together for her. That position also hits her g-spot as much as it can straight intercourse, so that helps too. And, she really enjoys that she can go at whatever pace she wants.
And that's the good news, of course! One reason I don't believe I'll ever be able to convince her on extended periods of chastity, though, is because there is no way that when we are in that position that I can hold out before she's done. Just never going to happen. That's why I'm really considering buying one of those penis sheaths (also called extenders), or something to cover me up so that I don't feel it to make me last longer.