Well, there are two different cases I use on a consistent basis.
Apple Bumper - I use the Apple bumper for a day-to-day case because it doesn't completely cover up my beautiful iPhone 4S. I'm super careful with my phone on normal business days and this bumper lets me lay it pretty much anywhere without worrying about the glass getting scratched. It also allows me to clean the phone very easily as most of the device is exposed for cleaning. For me, it also adds a bit of extra grip for holding the device.
Otterbox Defender - I also have an Otterbox Defender case for my iPhone when I know there's potential hazard. If I'm going camping, the Otterbox Defender case provides my phone with absolutely fantastic protection against dust, damage, etc. I also tend to use this on road trips, vacations, etc. as I never have to worry scratching it or dropping it and can just toss it in a backpack and go.
So there are my favorite iPhone cases!