Vaginal for sure, anal i have tried but both me and the girl at the time was not enjoyable... Vaginal is awesome! Having both the feeling of tightness and wetness around your cock while you fuck is epic! ^_^
For a long time, I greatly preferred vaginal over anal, almost exclusively. However, recently, my boyfriend and I made a small change which has made anal much more enjoyable for me. I still generally prefer vaginal though :)