7 plus because:
Most likely will have better battery life.
A10
Dat camera.
System wide support for higher gamut display.
Stereo speakers.
iOS standby battery drain is close to zero.
Updates
No issues with scratches on the screen, lag
No touchwiz
128 GB of NVMe goodness.
This is just based on speculation from the keynote. I've been an android user for the past 5 years or so and have never tried an iPhone. I'm happy with my oneplus 3 and won't switch it for any other phone anytime soon, but between these phones, I would have to choose the 7 plus.
I used Samsung for 3 years( S4 and then S6) and both were amazing phones. But they have been slacking since the S6. Note 5, S7 and the note 7 were incremental updates with just the specs changed. They are stagnating and it shows in the products.