I preordered the iPhone 7 and I think that it's going back today.
There's a lot that is better on the iPhone - haptic feedback that feels awesome, 3D Touch, reliability of TouchID, dual stereo speakers that are louder and richer sounding, snappiness and aesthetic refinement of iOS, always-on Siri, superior software support (I.e. more frequent OS updates), less aggressive sharpening in photos with rear camera, clearly better front facing camera, better standby battery life.
But there's also a lot that's better on the Samsung - the AMOLED display is just better in every way, the rear facing camera is superior in the vast majority of situations, fast charging is really useful, stereo audio recording in videos is way clearer than the mono recording on iPhone, longer battery life when the phone's actually being actively used, the presence of a back button, the presence of a headphone jack, Android's notification system, Android's file management system, Android's contacts system, the ability to set a custom ringtone.
My particular iPhone 7 suffers from loud hissing sound in videos recorded with the camera. It's very noticeable and clearly faulty hardware. It's quite widespread issue by the looks of it; even the well known YouTube reviewer Erica Griffin has noticed it in her review model.
The problem for me is mostly the additional cost and lack of enough compelling upgrades over the Samsung to justify it. There's a lot that's better but is there £700 worth of upgrades? Even if I sell my Galaxy S7 it'll still be about £450 to upgrade. And quite simply while there's a lot that's great about iPhone, I have come to the conclusion that I don't feel that there's £450 worth of improvements (and indeed even some noticeable regressions).