i had the original 6+ and then 6s.
6+ was completely unbreakable even after year1, the only issue was that it had 1gb of ram and safari/chrome always crashed.
6s+ had about 10-15% worse battery life, and after year1 with ios10 i think ive lost another 5-10%. I used to basically never end the day under 40%. Now i basically have to charge the phone every night. But the battery is still generally unbreakable over a 24hr period. I used to be able to charge every other day on weekdays, now i just plug it in every night.