This question should be answered not with a brand in mind but rather a protective case design. Brands aren't going to provide the best protective case design for any phone whatsoever but a design will.
In our opinion a case which is all inclusive, weatherproof, with rugged rubber on the most unprotected areas of the phone is the best case for an IPhone or any phone for that matter.
One can find these type of cases in general websites selling military grade protection for smartphones and whatnot.
