Depends what type of protection you're looking for? Just scratch protection? Or drop and scratch protection? Or do you want drop/scratch and water protection?
I've always liked the maximum type of protection, so I've always used the Otterbox Defender cases (I had o e on my 3GS, got one for my 4, and have one on my iPad). However, while the 3GS defender had decent water protection (not waterproof), the Defender for the 4 offers hardly any water protection (and I don't like the design of it compared to the 3GS case design...ice had some issues with it).
I am now going to try a LifeProof case, especially since I'm getting the 4S. If they live up to their claims, it should be a great case. It offers scratch, drop, dust, and waterproof protection. It's supposed to be waterproof to a depth of 6 ft. And all in a thinner body than the Defender. I hope it's as good as it sounds.