To be fair various ones like yellow screen or creaking or things of that nature have had threads about them pretty much with any versions of the iPhone (at least in recent years). There are threads with some types of issues or another type even with the "S" versions.I'm saying that I always buy the phone that has problems.
iPhone 4 - Antenna issue (4s fixed it)
iPhone 6 - Bending issue (6s fixed it)
iPhone 7 - Creaking, yellow screen, humming and animation problem (iPhone 7s will probably fix those things)
I'm gonna start only buying the "s" versions (also known as the fixed version of the previous iPhone)