I vote case...
Regardless of how it looks, you should get a case to protect it from drops, dings, scratches, etc. they are pretty sensitive. My cousin decided to go "naked" with his iPhone and just recently dropped it from less that a foot distance. It completely shattered... So to case is smart. Not to case is not too smart.
A bulky phone looks better than a broken, scratched, dinged, shattered phone any day!
I recommend otterbox. I have the defender series which is perfect if you drop or are afraid of dropping your phone. Well worth the price!
Beats having a broke phone. Then having to replace said phone after it breaks. Replacement parts cost the same or more than cases. I'd just go with a case.