Well I can only tell you that I have a 6+ and i think it is great. I do have big hands so I can mostly use it with one hand. I am a heavy user in my opinion and the battery always lasts all day. Sometime I can go to be and still have 50% left. If you want better battery life go for the plus. If you want more pixels then get the plus.
Currently running iOS 9.1 PB on my 6+ and I've still got 69% battery life remaining (and that's with Bluetooth enabled). Vastly superior to iOS 8.4.1!