When I bought my OnePlus 3T I knew I had to buy a case as every phone I have bought without a case before has broken.
I did a lot of research on the subject and ended up selecting the Spigen Ultra Hybrid case and I am certainly glad that I did. the back of the case is hard poly carbonate while the edges of the case are made of clear thermoplastic polyurethane. The edges on the screen are slightly raised to protect the screen from drops.
Many people make the mistake of buying a case without a raised bezel which does not protect the screen at all. The raised bezel takes the impact of a drop flat on the screen. Without the raised bezel the screen is still going to crack and you might as well have not put on the case at all.
This is also an extremely thin case and does not add much to the case at all. It is also a great value and does not break the bank.
Best of all the fact that the case is completely clear shows of the beautiful design of the OnePlus 3T.
Instalation: It is important to note their is a thin layer of plastic you are supposed to remove from both the front and back of the case, so if you see imperfections on the case when you receive it, it is almost certainly that removable plastic, which can be hard to realize it is there.
Verdict: If you have a OnePlus 3T, Buy the case.