I got the gold 6+. Space Gray just looks sooooo boring to me. I actually like the white bands on the gold. Yeah, they stand out more, but they also look more like a deliberate design decision. Like they wanted those lines to be there from the start and they match the white bezel. On the grey and silver models, the bands look more like an "ooops, how are we going to hide this mess? Let's try to camouflage them and hope nobody notices...". As a result, I notice them way more on the gray/silver back than the gold. Funny how the mind works.
I am a bit concerned that the gold 6+ might look too much like a tacky gold brick when I get it. But that's what cases are for and I don't see myself using it naked. With the right case and color, I have a feeling that the gold has much more potential to stand out and look cool than silver or gray. Cobolt or egyptian blue, royal purple, ruby red, black or even green could look really stunning with gold accents. I do agree though, the gold 5S looks a lot more classy when naked than the 6/6+ does.