It doesn't matter! You will get colorblind within a few days, and not even think about it.
First question you should ask yourself: can you look your male friends in the eyes when you put down your white phone on the table?
Second question: If "no" is the answer to the first question - does it even matter, when the girls will be all over you and your white phone?
I suggest that you choose a black one. I agree with people who said that the color looks more manly. If you look at the white one, it looks as if it was made for a girl (just my opinion though).
I'm a guy and I also have the white iPhone. I personally prefer to be different then everyone else and seems like around me everyone has a black iPhone and plus I kinda like the white look of an iPhone.