As some others have said, cowgirl facing me, so I can suck on her tits (and/or kiss her) while she grinds her clit on my pelvis. Having her ride my face is a close second.
Reverse CG is nice too, being able to suck on her neck and shoulders while working tits or clit, but most of the women I've been with usually want to be facing me, so I haven't done it a lot.