I have always used Spigen cases as of late. They are my go-to case manufacturer and I've preferred their look, feel and additional features.
I used the Slim Armor with the G4, the Neo Hybrid with the ill-fated Note7 and my current go-to is the Tough Armor for the Note8 although I have a Rugged Armor as well.
I can comfortably recommend those for the S9. The Neo Hybrid if you want grip, Rugged Armor for an understated look, and the Slim/Tough Armor if you want protection without excessive bulk and a kickstand.
Of course, if protection is everything for you, then I would suggest the Spigen Pro Guard or Reventon. They are really, REALLY expensive at $60 and $65 respectively, but these are cases that eschew sleekness and design for protection. They even have a glass screen protector that attaches to the case frame.
UAG, Otterbox and even Samsung themselves make nice cases, especially if you have different aesthetic preferences or you want a different look and feel. But I have had more experience with Spigen and those are the ones I can recommend