Just as a disclaimer, I personally have used neither, however after talking to those who have, I would recommend the otterbox - if your main concern is protection. Thing is that it makes your already relatively large phone a brick. Now for me, and this may or may not be the same for you, I am constantly taking my phone case and back cover on & off because I am always swapping the battery, so something like the otterbox defender case is not as practical for me because it would take a bit more effort than I would enjoy just to swap batteries. The UAG is a bit easier to take off (as I am told) but is probably not going to offer the same protection that the otterbox is.