Ok so figured I would chime in here being as I have owned both cases for the iPhone 4/4S. I much prefer the LifeProof case. For one it is much thinner and less bulky than the otterbox. It gives a great deal of drop protection too. I can't tell you how many times I saw my wife's iPhone tumble to the ground onto super hard surfaces with the LifeProof on and there was not once a bit of damage. The phone literally looked brand new after two years of hard use. Waterproofing was also a great feature and living in South Florida we did make use of it regularly with swimming, jet skiing, going to the beach etc. I am really hoping that their new version will live up to the old one, and hopefully be even thinner for the iPhone 5.
The otterbox for the iPhone 5 is nice. Good build quality. Seems like it would protect well. Not waterproof however. It is bulky, although not quite as much as the one was for the iPhone 4. The belt clip is nice too. I guess my real grip about it is that because of its bulk, you really cannot tell that you have this nice beautifully thin new iPhone 5 in there. No one who saw it in this case new it was a new iPhone. Everyone was like, I thought this was supposed to be thinner than the 4??