My 3G, 4S, and 5 were all white, which I think overall is much nicer looking and I always thought the black/slate looked ultra cheap. I debated white again for my 6, but since the space gray is finally so light it's close to raw aluminum, I decided to give the space gray a try. Love it, but still think I'll go back to white for the iPhone 7.
iPads are different though - my iPad 4 was black which was great since the aluminum was still raw aluminum, but I went white this time for my Air 2 because even though I like the light space gray on the iPhone 6, I hate it on the Air 2 because the chamfered edges in space gray look like crap IMO. But next iPad Air 3 will most likely go back to black, but we will see.