My only preference is that a guy dress how he LIKES/feels and is just himself. And I don't feel that any of those styles are really mutually exclusive. I like variety and contrast. I don't have the same style from day to day either. I would be so bored if I stuck to one thing all the time, or never mixed 'different styles' together.
I LOVE goth/punk/emo/skater/ dark mysterious rocker type of guys! Piercings, tattoos, black clothing, the whole package! There's something so hot about them I can't even begin to describe it. Snakebites and lip rings get me every time!
I like athletic guys because they seem strong, and can protect me. I like rocker guys also.
Definitely not preppy. Yuck.
I wouldn't want him to necessarily fall into one of those categories, but just have his own style. If he dresses nicely and looks good in what he wears, that's all that really matters, I guess. I do tend to find the rocker look pretty attractive, though.