Susan James

In both positions, the guy on the bottom has his movement somewhat restricted because of the weight of girl on top, so he can’t thrust as hard and deep as the guy on top. On the other hand, the guy on top can thrust hard and deep. So the cowgirl position allows for deep anal penetration, while the reverse cowgirl position permits deep vaginal penetration. Also, the cowgirl position is somewhat the more stable and comfortable of the two, an advantage for longer sessions of DP. The reverse cowgirl take a little more practice and balance, but it makes it easier for the girl to play with her clit during penetration.

Both positions work well and I like to switch between the two when I’m having a DP session, but I slightly prefer the reverse cowgirl because of the easier clit play and it also feels more open and vulnerable.

(http://www.autoadmit.com/thread.php?thread_id=3902759&forum_id=2#35477659)