Spigen Rugged Armor ($12)
Another solid choice is Spigen's Rugged Armor. It's their number one selling case, and for a few reasons. It's thin, durable, minimal, stylish and doesn't cost very much money.
The Spigen Rugged Armor is a lightweight and thin case made out of pure 100% TPU. They use the finest material that won't discolor over time, it's flexible and easy to install, and they've reinforced the corners for added drop protection.
This case has impact-absorbing dual layer sides, glossy accent corners, and faux carbon fiber styling at the top and bottom. It's a case design you've probably seen a few times, as most cheaper brands copy it. Don't worry though, this is the original, right from Spigen, for your Galaxy S9.