Have used both. Both have their place. Otter box for impact resistance. thicker, more flexible rubber protection. Life Proof for water/submersion protection, and for dust / particulate protection.
While I never had an iPhone crack in a LifeProof case, the Otter box definitely has better padding. However, the open hole in the Otter box screen protector for the iPhone start button is an easy access path for water (eg: in a sweaty pocket while working or exercising) and for particulate debris such as sawdust. PITA to have to pull the Otter box apart every day or two when working on the sawmill to clean the screen. Never had a problem with debris getting INSIDE of a Life Proof case.
My opinion: Otter box for casual phone usage. Life Proof for "Go anywhere. Do anything." type phone usage.
