5/5c/5s are all fine phones (though with the caveat that you should avoid the 8 GB 5c model like the plague...16 GB is the barest minimum that's adequate for iOS firmware). I'm still on an iPhone 5 picked up a couple of months after launch--in fact, all of our entire extended family is using the 5, with the only exception being an iPhone app dev; he's upgraded to a 6+, of course.
The 5 series are great workhorses that take advantage of LTE speeds, do reasonably well on the latest firmware, and are probably good for another two years for many people. I wouldn't consider a 4 or 4s at this point, but the 5's are still very usable devices.