Obviously, Samsung Galaxy A6 Plus is better as it has a bigger screen, better processor, bigger storage and much better camera quality.
To see the full comparison between these devices: Samsung Galaxy A6 Plus vs Samsung Galaxy J7
Samsung Galaxy J7 vs Samsung Galaxy On7 Pro
Both the phones have their pros and cons, I think you should go for samsung j7 2015, samsung j7 2015 has the following advantages over on7 pro
1. It has Octa core processor which is better that on7 Pro ,that helps the tasks to do in parallel without slowing down.
2.It has faster CPU,that means,more smooth experience
3.It has Has Front Camera Flash,that would be great for selfie lovers .
It is not like that it is a one sided game, on7 pro has the following advantages -
1.It has better RAM,More RAM means more applications can run at the same time,
Verdict - In my opinion, samsung j7 2015 is better overall performance and price ,if you need better RAM than go for on7 pro
You can also compare these devices on 91mobiles
I couldn't find any major differences between them. On8 has better display than J7 2016 and J7 2016 has better processor than On8. I'm using J7 2016. Its performance is very good. I have seen On8 also. J7 2016 is slightly faster than On8 and has better graphics too. You can go through this comparison too. Compare. I'm attaching a video which I just found on YouTube. This might help you in picking a best one.