S8+ has a bigger battery capacity and will probably last longer like the iPhone 7 Plus had over the 7. And the keyboard in portrait mode would feel a little roomier.
With that said, I do prefer the size of the S8 which has the same width as an iPhone 7. I can't believe someone referred to it as "compact" when it is still quite a tall phone and has a 5.7" display.
I got used to big phones pretty quickly but my max size is close to 150 mm in height. Anything taller becomes an issue when reaching for the top.
I went with the plus model....the thing is stunning but it doesnt feel like its 6.2" when it sits next to the S7 edge. Overall a thing of sheer beauty regardless which size u choose
What's the point of launching two device with only .4 inches screen difference? They both are in the big category... maybe Samsung research showed that there is very little demand for small handsets!