I put the OtterBox Defender case on my S6 the day i picked the phone up. In the colder months i leave the case on all the time. When it warms up, and i don't have a jacket on with a pocket to slip the phone into, then i frequently take the case off when i go out.
I like the toughness of the Defender, as well as the protection. But the screen protector causes me a lot of issues in the sunlight. It is quite difficult to see the screen, so i am constantly trying to shade the screen so i can see. Being that i work outside for a living, a tough case, ideally WATERPROOF, is a necessity, bit seeing the screen well is also crucial.
Given my dislike for the issue i have with the Defender case, i bought a Ballistic case and tempered glass screen protector at BB yesterday. Yeah, it cost me $80, but i can see the screen much better, it fits in my pocket pretty easily and i still feel that i have pretty good drop protection.
Now, i am anxiously waiting to see what Lifeproof and OtterBox do for a waterproof case.