Vagina, all the way.
Fun story. I used to work with this gay man, and him and I were pretty good work friends. One day we got to talking, I asked him if he'd ever had sex with a women. He said "no I'm gay, I don't like that." And to that I replied, yeah but how do you know you don't like it. I've never had sex with a man, but I have had anal sex with my girlfriend so I know what both holes feel like. He ponder that for a bit. And the next day he came to work and said, "I'm going to have sex with a woman tonight." He had asked a friend of his if she'd be willing, and she agreed. I didn't see him for a few days, and honestly I had forgotten about the conversation, but the next time I saw him at work he came up to me and said "yeah....I'm bi now. That was awesome!"