On cases you have two choices.
The larger and more bulky cases like the Otterbox offer the most protection but make you phone huge and brick like.
Sleeker cases like the Barely There do nothing for drops but will protect against light scratches.
Check out the accessory forum and there a lot of details
I find that smaller cases do protect from drops, but only certain kinds.
Myself, I'm using a thin, clear, acrylic case that only covers the back and sides and gives the phone a small lip in the front. That's all the protections I really need.
If I drop the phone on its face, the screen is going to be cracked. I know that. However, if I drop the phone any other way, the acrylic will take the blunt and, although the force is generally not absorbed, the phone itself won't get scuffed or broken.
Plus, I'm not one to throw my phone off of a table. If I drop it, I'll catch it with my foot before it hits the ground.
I also don't have my phone in my pocket or anything when I'm moving at higher speeds (bike), so it's only stationary drops that are possible.
All in all, get what is comfortable for you. I also have a silicon case that provides complete protection along with an Incipio Feather. All are thin and all are great at providing protection.