Similar screen tech, the same processor and similar-grade cameras make sure theres no weak link here.
However, I do like that the extra display space of the iPhone 6 Plus and its greater battery life makes it more of a power user device.
I'd opt for the iPhone 6 Plus over the smaller iPhone. But I've loved using both. For the better display, battery life and camera, go for the 6 Plus. If you can live without two days battery life and far from fantastic low light images, then the iPhone 6 is a better fit.
iPhone 6 vs 6+
Apple IPhone 6 Plus 16GB vs Apple IPhone 7
Both the phones have their pros and cons,Lets analyze:-
Advantages of Apple IPhone 7
1.Quad Core CPU:-More cores result in better parallelism, meaning more tasks can be processed in parallel without slowing down the User Interface.
2.Faster CPU:- Faster CPU means more smooth experience.
3.More RAM:-More RAM means more applications can run at the same time,
4.Supports VoLTE-Apple iPhone 7 is VoLTE Enabled. You can use this to make calls over 4G network. It is compatible with Reliance Jio.
5.Light Weight:-Light weight devices are easier to hold without tiring your arms.
6.Better Camera Resolution:-More resolution generally means better picture quality,
7.More Storage Capacity:-More memory allows you to store more songs, videos, photos and install more applications.
Advantages of iPhone 6 Plus :-
1.Bigger Screen:-Reading, browsing internet and watching movies is more pleasing experience on a bigger screen.
2.Better Screen Resolution:-More resolution means sharper and crisper screen.
3.Bigger Battery:-It can generally last more time.
Verdict - In my opinion, Apple IPhone 7 is better overall performance and price ,if you need bigger screen and better battery life you can go for iPhone 6 Plus
You can also compare these devices on 91mobiles