My preference colour GOLD>SPACE GREY> SILVER...
MY OPINIONLOOK at the white band, GOLD + WHITE makes the perfect contrast out there...
Next, you look at the camera lens, covered with GOLD RING, touch ID GOLD RING, PREMIUM enough

For Space Grey, In my opinion, BLACK iPhone is very lasting (lasting in terms of the color wont make you feel boring even after a year?)
Why i not go into SPACE GREY for my upcoming phone is, The contrast line is too dull between "SPACE GREY and GREY?"
But not to deny, black iPhone is very well matching for almost all the cases in the market
For Silver, Its still look elegant and nice tho, but i am not into it is, i prefer "GOLD-RING" for the camera and touch ID

For some reason, when the light reflect to gold TouchID. It looks like silver