First Hentai I've ever watched was a Futanari. Title was: [b]F3: Menage a Trois[/b].
Seen it when I was in Highschool. Got it from my cousin and I watched it with my sister. It was so, so funny and weird.
This is the synopsis.
[spoiler]Hiroe Ogawa is one frantic, frustrated female (hence the title F3). Physically perfect in every way, this nubile beauty suffers from an inability to, um, reach the peak of physical pleasure. So, in attempt to achieve the desired state, our delicious heroine exhausts more sexual possibilities than you can shake a stick at trying to get her horse over the hump.[/spoiler]
It got to the point where the Hiroe got possessed and grew a D so she could experience orgasm. Hahahahaha.
Anyway, my favorite is [b]Vanilla[/b].
I prefer Pettanko than Oppai.
I also like Chikan a bit.