This time around its less about color and more about 6 Plus 128GB capacity since I put a case on my phones anyways. My work phone is a 4S in black so no biggie.
Space Gray for me. I had the gold and enjoyed it but hated the white front. I think a gold with black front would look pretty sick but that'll never happen. And the silver looks tacky to me.
Lots of ways to be unique... iPhone is not one of them ;-) Go for face color you prefer (white vs black), then go unique w/ case. In any case, you'll still have newest iPhone ;-D!
Going with space grey. The white front of the silver and gold makes me think the glare will hurt my eyes after a while. I prefer the black front so the screen has a kind of frame around it.