I was a long time iPhone user, and switched over to the S8 in October. To be honest, I have mixed feelings about the switch, and may actually consider going back. Some observations, all my opinion.
I have a lot more trouble with the compass in Android and the bearing / heading in an app like Gaia than I ever did with iPhones. With the iPhone, it just worked, not always true with Android. Noticed this with a friend's android phone too.
The built in notes app for apple worked a lot better and more seamlessly than OneNote which is what I'm using now. I spent 10 minutes trying to get the damn thing to select the right text I wanted the other day and have no idea why it wouldn't work. Something that never happened to me on iPhone. Sync isn't always automatic either between phone and my Macbook.
My android phone randomly erased itself and everything on it sitting in my pocket one day out hunting. If that every happened when I was in the woods for an extended trip, I'd be F**ked, and pissed if I lost all my photos, waypoints, etc.. Literally - I had NOTHING. Once on network, basic stuff came back, but I still lost a lot of stuff that I wouldn't have with the iPhone
Phone Backup through ITunes works MUCH better than through Android if you want everything on the phone backed up. Seriously - if I got a new iPhone, came home, plugged it into my laptop. Everything from the backup would load in and there wouldn't be a thing missing from photos, text messages, etc...
I still haven't found a mail app that works quite as well as the integrated mail app on iphone. Maybe I was just used to it.
The fact that apple locks down car play SUCKS - no way I'm using apple maps. Waze and Google Maps with me - so basically means no CarPlay for me with an apple phone. I mount the phone next to my steering wheel.
Love wireless charging on my S8, but apple has that now too.
I do like the Google Integration better with Android, including Google Photos. Didn't use it with iPhone and haven't looked to see if it was available.
Have had on and off weird notification problems and battery problems with the S8 that were much easier to resolve, or just didn't occur with the iPhone
I do like the S8, but felt like the iPhone always just worked.... Much more "seamless" user experience across the board.
If your an apple user, unless you have a real defined reason to switch, I personally wouldn't.