I just (1 1/2 weeks ago) got a iPhone 7 Plus. This is my first ever iPhone after having Andoids for a zillion years. I just had a S8 and gave that to my gf. So here's my take on them.
The S8 is a beautiful phone, however I've never liked liked amoled screens and their blown out colors. Also amoled screens , to me, look "flat" like everything is painted right on the screen surface. LED screens, to me, have a little bit of a "3D" look to them, like they have some depth.
The S8 is Samsungs fastest phone that I've had (had s4,s5, s6, s7e and S8).
I'm not particularly a fan of the curve screens. Palm rejection seems better on the S8 than the S7E as is the battery life.
The iPhone 7 Plus is also a great looking for with perfect craftmanship. The screen display is the best, for me, of any phone that I've ever had. The display supports sRGB and DCI-P3 and iOS has a color management system whereas Android does not.
The 7 Plus is warm butter smooth and (to me all this post is imho of course) iOS just feels much more consistent to me. Android now feels like so many pieces just kind of screwed together.
The main reason I got the 7 Plus is for the camera. This simply (remember imho) is the best camera in any phone that over ever had. Just even with the native camera app the jpgs are very, very good. No crazy oversharping like most other phones do these days.
So this switch for me has been the best chenge I've ever done. On a phone, the camera is the number one consideration for me and this phone, so far, has simply amazed me.
Battery life easily gets me through a day with plenty left at night still. Again, better than any phone I've had before, even the S8.
I just got another update a few days after I got the phone so I don't know how much that contributed to the overall phone and camera usage.