iPhone 6S, 128GB. As good a phone as it has been, I am now on my second replacement since purchasing on launch day in 2015. The first replacement was in Jan of this year due to the battery defect/early shut off issue. Then this past week, while I was browsing on safari, the phone began to heat up and then the screen went out. Took it to Apple Store and they tried replacing the screen but the phone still would not turn on, so that meant replacement phone number 2.
Fortunately, since I never got a Plus version of a phone, I won't miss anything when it comes to screen size when going to the X. I will only gain.