Spigen Rugged Armor
The Spigen Rugged Armor is one of the most popular case styles on the market, from one of the most popular case makers. Period. If you're looking for an excellent case that's slim, easy to install, durable, and affordable, this is it.
Spigen uses precision-cut soft and flexible TPU material that perfectly matches every phone. This case is so popular, in fact, that multiple other companies copy the exact look and feel of it.
That said, if you want a great case from the original source, consider the OnePlus 5T Spigen Rugged Armor case.