2 piece or one piece doesn't really mater for me. If she has goodies on her, I'll be admiring her and of course thinking about having sex with her, and if she is one of those long term relationship looking girls I would think of having her as my wife.
I imagine how she would be like without anything :P, if the girl is hot. I prefer small/medium firm breasts, so if the girl has that I imagine how it would be to fondle and play with it. Also, a cameltoe is a added turn on, sends my imagination wild :P