The best case type is which ever one you like the most. You are going to get a ton of different opinions on this here. You are going to end up doing what most of us on this forum have done. Buy 10-15 different cases, spend a small fortune, and still not be satisfied.
more about durability really, I have a silicon skin currently wrapped round my first gen iPod, with the iPhone being a phone I wanna be a bit more protective of it lol