I have the S7 Edge Blue Coral and it was great for a month or so until that lagged came back. I need to factory reset it once a month/two months, so blah with that. I also got tired of the curved screen.
I got the Mate 9 just to give a try, thinking I most likely would take it back. I had previously bought the Axon 7 which I really liked, it had the best speakers of any phone I've owned. I was going to keep it but I had trouble sending MMS, T-Mobile nor Axon could figure out why. So I gave the Mate 9 a try and I love it and decided to keep it.
I love -
the battery life,
the screen size,
it's fast, zero lag and promisses no lag for at least 18 months,
the little options it has here and there,
screen to body ratio,
build quality,
descent speakers,
fast charge,
overall feel in the hand,
super fast fingerprint scanner,
camera not better than S7 edge but it'll do,
picture editing tools,
no issues with the screen resolution, specially if it helps with battery life,
screen capture from drop down bar,
pressing volume down twice to trigger the camera when screen is unlocked,
all the battery saving options,
navigation bar switcharoo options,
I actually like how it looks without a case
I would not go back to the S7 Edge. I have the S7 edge on JUMP ON DEMAND so I'll definitely try the S8+ when it comes out but I'm very happy with the Mate 9.