iMessage with a friend or significant other is a lot of fun between the stickers you can send each other and GIPHY and music and stuff that I've made fun of in the past on this forum. And of course it's great for more professional communication with groups of people.
I got the iPhone 7 Plus and the display is beautiful. The camera is finally how I want it. I think the thing my Samsung is better at is recording video with better sound. The actual visuals, iPhone 7Plus does better, but my Samsung gives me amazing multidirectional sound. And it works better as a phone. My iPhone conversations can be pretty choppy sometimes.
Still, it's a good refinement over the iPhone 6S Plus I had and leaps and bounds better than my iPhone 6Plus.
I don't think I would trade my 7Plus for an S8 at this point if I could have only one. If I had to go to only one phone then I think the choice might come down between the iPhone 7Plus and Note8 or S9...when they get the fingerprint sensor located in a better place and refine anything that might be annoying in the S8.