^^^This re: raised backs. Two current case below have this.
I have a love/hate for clear TPU cases. Had one on my iPhone 6 Space Gray. After about four months, it started to yellow on the back of the case, right where the CPU was located. And with the silvery gray back, the yellow showed. Maybe not really noticable, but was bugging me. Eventually replaced it with what was supposed to be a black frosted case, but was more a smoke color, imo (Luvvitt?) Looked good, kept it: worked well and thin.
Guessing the silver 8 might be prone to showing any yellowing.
I have had Luvvitt, Spigen, others. All worked well. Only one that I did not like was a hard plastic case that started to crack on the corners (ip 4S). Never will do hard plastic again.
I had bought a Spigen Slim clear for the 8. Clear, not overly thick, but has decent sized bumpers on the side. Adds a decent amount of protection without any bulk. Complaint: gives the phone a retro 3G look. A bit distracting, imo, the way it shines. As the plastic ages and is used, might dull, so might be a short term distraction.
That said, bought a barely there clear TPU case at Fry's today. Some no name company made it. Like the look of it much better (less shiny TPU on the sides), and feels so much closer to like the way the phone feels when you pull it out of the box and put it into your hands. With a blackish gray back on this years SG, hoping any potential yellowing will not show.