An otter box because they were made at first for the army but you can pick out any color you want but that is what i have for my iPhone 4 and I dropped it in a mud puddle the other day and it is totally fine and they made make cases for most phones so good luck.
The Otterbox, or if you cannot afford one, try going to your local stores such as, Walmart, or go to a phone case shop and find the best military phone case to ensure durability, if you cannot afford a Otterbox. Otterboxes usually range around 50-80$ depending on your phone. But military usually 20-30. And they work just as good.