Who should get the space gray and black iPhone 5s?
If you want a color that won't distract you when you game or watch video, that absolutely won't discolor, even if it does show wear and tear a little more visibly, that's closer to timeless even if it's also more reserved, then get the space gray and black iPhone 5s.
It's the classic for a reason.
Who should get the silver and white iPhone 5s?
If you want a color that draws more attention in its own right and stands out better from the crowd (without being overly fussy about it), that may be more of a distraction but that doesn't show damage as much, then get the silver and white iPhone 5s.
Apple's senior vice-president of design, Jony Ive, is most often seen with it, after all.
Who should get the gold and white iPhone 5s?
If you want everyone to know that you have the latest, greatest iPhone 5s, and you want to stand out as much as possible while doing so, that you're also not as easily distracted and enjoy that it doesn't show damage as much, then get the gold and white iPhone 5s.
It's the bling thing.