Doggy, because I love womens’ asses, and the feeling of it pressing against me.
Froggy- see above, plus a little bit of extra friction between the cheeks.
Cowgirl, when she really gets into it, grinding her clit into me, and a watch her face when she cums then collapses on me.
Missionary, so I can watch her beautiful expressions and cum while making out with some passionate DFK, ups the intensity and intimacy. Sometimes with my hands on her ass (to maximize Gspot stimulation), and with a partner that enjoys it, teasing her “o” with a finger till she cums hard, and if you are lucky, squirts a bit.
Meh, I can’t pick a favourite.