I can't vote, I'm too indecisive.
I've only ever had 2 iPhones (3GS & 4S), and they've both been black.
I'm leaning toward white/silver this time around; but if last time was any indication, I first pre-ordered a white, then cancelled it to pre-order black!
But I think this time I *might* just make it to white/silver!
I don't like that the black/"Space Gray" is pretty much all black/gray and isn't accented with chrome antenna bars around the perimeter like the 4S was. You can't barely even make out the ID ring around the home button on the black/gray one. I didn't like the black 5 as much when it was released. I'll need to see the 5S black/gray in person.
EDIT: Saw the "Space Gray" in the store today and it was very sexy! I like how the hue of the bars & back are offset from the rest of the black, unlike last year's iPhone 5 black. If I can't find a silver, I may buckle and take the Space Gray.