It really depends on the person/cock.

I don't size-shame, but if the person has a slightly smaller cock, doggy will probably just work better. There's just better...leverage?

Also depends on how comfortable I am with a person. It took me a while to get comfortable riding with one guy. It felt super emasculating to intentionally bounce on his cock and I didn't know how to let myself be that vulnerable in front of a guy until I took the plunge. His immediate enthusiasm soothed any worry I felt and it was incredible to ride at my own pace until we both came.

It also depends on how intuitive and compassionate of a dom the guy is. I like doggy because I love when a guy takes control! But...dude's also gotta read my body and make sure I am not tense and it isn't hurting at all. Takes a bit of trust to let a guy go to town on me from behind. Once there is some trust, I am super content being bent over on all fours.

I love both, but which one I prefer depends on the situation.