Vaginal of course. It's natural and romantic. Anal just feels kinky and "forbidden". But I prefer to save it for rare occasions, such as when I'm horny but her pussy is sore. I'd surely be wanting to do more anal if my girl wasn't on birth control though, that way I could still cum inside her. (tip for girls whose boyfriends always bother them with anal: get on BC and tell him how sexy it would be for him to cum in your pussy)