I recently auctioned for and bought a $200 (USD) iPhone 5s on eBay for a friend of mine that wanted to upgrade from an old Android phone that couldn't even install Facebook because the Facebook app was to big. The 5s has a good 3-4+ years of upgrades left in it while the 4s will probably not upgrade to the next iOS version to be honest.
Also, if you ever buy accessories for your 4s, they won't be compatible with any future upgrade you may want to get since nothing released now uses the 30-pin dock connector. This would mean that any cost you save by getting the cheaper phone now will be flushed down the toilet the next time you get a phone if you buy power cords, etc.
Also, if you ever buy accessories for your 4s, they won't be compatible with any future upgrade you may want to get since nothing released now uses the 30-pin dock connector. This would mean that any cost you save by getting the cheaper phone now will be flushed down the toilet the next time you get a phone if you buy power cords, etc.