Spigen Rugged Armor
Spigen is still one of my favorite brands when it comes to smartphone cases. They typically offer 5-6 different styles and options to fit the needs of any and all customers. For those wondering, they no longer sell on Amazon and have moved to eBay, if you couldn't find their awesome cases.
The Spigen Rugged Armor is the first case I get for almost every phone, and the OP3 was no exception. It's thin, smooth yet grippy, has a neat carbon fiber look at the top and bottom, and most importantly wraps around the sides of the display for complete protection. Spigen needs no introduction, but if you haven't tried them before lets just say it's worth the $11. This is what I'm using as we speak on my own 3T.