I did go from a 5 to a 5s.
It was reckless extravagance, so I hesitate to recommend it to others, but I'd do it again.
Camera takes nicer pictures, TouchID is awesome, and the band availability is much wider. On a non-Sprint North American 5s (A1533), can go on Verizon, AT&T, or T-Mobile Stateside, or on the Big Three or Wind or Mobilicity or the regionals in Canada.
As others say, you're paying the subsidy anyway so it makes sense to upgrade if in the USA, and then sell one. (Probably could upgrade to 5s and get the amount paid flat for your old 5, making it "free" -- no cash out of pocket, but two years more commitment.)
Only reason not to would be if you want to get a 6 for sure and you can't use a family member's upgrade next year. Although, again, the upgrade and sell method seems to work for many.
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