There's no denying the Galaxy S8+ is the way sexier phone but ergonomically, its length makes it a bit awkward to operate one-handed in vertical mode.
While the iPhone is heavier, but the width and length still makes a quick-draw selfie fairly easy compared to the Galaxy S8+. Sexy as it, it was also slippery around the edges and the best fix would probably to get a case with a bit more grip.
Or grab a selfie stick and risk the judgemental stares of the people around you. Still beats having to repair the phone if it falls out of your hand, though.