Both the phones are almost identical in weight and also blessed with almost similar image and camera quality that is hard to detect from the normal human eye. Though, iPhone 7 has a better camera pixel and auto-focus as compared to 6s plus, however, the 7 is still better though people will more prefer to buy 6s plus or 7s plus due to the variable budget range.
Though iPhone 7 has some great advantages if you previous have had hold an old iPhone 5s or will be buying the phone for the first time; it is still a rock-solid phone. The 6s plus is shipped with the old processor and 7 is still a powerhouse in terms of the new and extremely fast Apple processor.
Though the A9 chip in 6S plus still does not lag behind as compared to its successor, you can also pick iPhone 6s Plus 64gb Unlocked which is the best buy in this segment.