When I'm on top, I almost always go cowgirl. It's just better for me, and since I'm on top I do it the way I like.
The "cowgirl or reverse cowgirl?" is more of a question for me whenever we're discussing having a DP. Cowgirl is an easier position. Sometimes I'll start off with me doing cowgirl, the second man will lube up his dick and my bum, and we'll go at it for a while, but then switch and I'll do a reverse cowgirl anal (same guy, no pussy/bum switching) so the other man going into my vagina can move himself more. The reason is when I'm doing regular cowgirl the man in my bum usually comes pretty quickly, while the guy in my pussy, who isn't able to move as much, and I don't orgasm and have to finish separately. With reverse cowgirl anal, the man in my pussy can work our genitals so we both orgasm, while the guy in my bum with constrained movement is slowed down and matches the orgasm timing more closely.
It's taken us some time to work this out. Most of the time we have sex, however, it's either just MF or FFM.