I use magnetic wallet cases (without any latches or buttons). They give you full 360 degrees of coverage without having to put anything on the screen to get in the way. The case also doubles as a stand and folds perfectly flat on its back without any arch for typing. I've been using a few of these over the years on my 6+ and it looks perfect to this day. No scratches on the screen. I've dropped my phone over a hundred times since 2014 and it looks like day 1.
My family also has iPhones and they each have their own things like full on Otterbox Defender, to a combination of rugged case with a screen guard, and other 360 cases with a magnetized latch. I still prefer my case style the best. I never run into problems with dust bubbles and rainbow effects that develop with other cases. In some cases with other cases, it goes away with some effort, while with others, it can still linger on permanently. On my iPhone, I simply wipe the screen and its perfect again.