We've personally owned just about every model iPhone since the 3GS, or I've had one for development purposes, I've also had several Android devices from Moto and Samsung - I've done development on both platforms, installed custom ROM, JB'ed, updated to x.0 versions of the OS, run betas, and I've _never_ had anything near the level of issues being described by some folks in this thread.
I find it astounding they'd have multiple devices/replacements, and continue with the same issues, *and* have friends/family experiencing an even worse issues.
My wife and I have used our 6S and 6S+ non-stop since Saturday a week ago, and I've had maybe one or two, unique, nonrecurring instances of a problem (and AFAIK, the wife hasn't had any).
We've shot photos, videos, shared via AirDrop, sent dozens of emails and messages, done some video editing, recorded notes, recorded and shared audio, played a few games, AirPlayed Cinemax to our Apple TV, used cell/wifi/BT, connected via USB, played music, I've managed AWS services and used DropBox and GDrive, listened to Podcasts, slept all night with a T-storm sound app - and just really _no_ issues.