I hate cases, so this is probably the first time I would have checked "Using a case" in a poll like this. The only reason why I got a case for my S4 is because of the camera on the back. It sticks out, which means the phone is always resting on it. I picked up the Spigen Neo Hybrid because it's thin, has button extensions, and the lip around the screen isn't that intrusive. It also, most importantly, protects the camera better than without a case.
I usually have the ninja death grip on my phones when pulling them out of my pockets. I never had a case on my previous phones (BB, iPhone, Nexus4) so having a case on my S4 is new to me, taking some time to get used to it. With this new case, the sleep/wake button is easily pressed, I do it every time I pull it out of my pocket. Gotta be careful, but overall I like it.