For me? 69, hands down. I realize that's not a favorite for most women, however.
Amongst penis-in-vagina positions, it really depends on what gives my partner the most pleasure. I've been with a woman who could cum consistently in the missionary position, every time. We might start in other positions, but always had to finish in missionary. I really came to learn how to move and thrust in ways that maximized her pleasure, and being on top gave me more ability to control my orgasm and time it so we'd be within seconds of each other. On the other hand, I've been with another woman who always had to be on top, grinding her clit against my pelvis, and having me suck madly on her tits. I've also been with women who needed things mixed up a bit, or were often searching for and sometimes challenged to find the position that would best get them off.
Haven't been with women who preferred reverse cowgirl or doggy, though. At least the women I've been with prefer kissing and eye contact most of the time.
In any event, always happy to oblige any of the above.