LifeProof and OtterBox are both smartphone cases designed to protect against drops and water damage. While Lifeproof only manufactures cases for iPhones and other Apple products, Otterbox is available for Android smartphones as well.
The OtterBox comes in various different series. The case that is comparable to LifeProof is the Armor Series. It is also available in less resilient, cheaper series called Defender ($49.95 - $59.95), Commuter (34.95), Reflex ($34.95), and Prefix ($24.95).
LifeProof is waterproof for half an hour, up to a depth of two meters, and can protect against drops of up to 6 feet 6 inches. It also allows users to take photos underwater and has a swimming headphone adaptor. It adds 1.5mm to the thickness of the phone, and it also functions as a subwoofer to improve the bass and mid-frequency sounds from the iPhone speaker. The case is available in black, white, cyan, brown and magenta.
OtterBox is also waterproof for half an hour, up to a depth of two meters, and can protect against drops up to 10 feet. The headphone and charging ports are accessible through watertight rubber flaps.
@JoeGlock730 explains the differences between the two cases:
Here are the front and back views of OtterBox and LifeProof cases (click on the image thumbnails for larger views).
LifeProof is shock, water and dust resistant. It meets Military Standard 810F-516, which requires that it can withstand infrequent, non-repetitive shocks.
OtterBox is also shock, water and dust resistant. It can withstand drops of 10 feet and 2 tons of crushing force.
LifeProof for the iPhone 5s costs $89.99 when bought directly from the company.
The OtterBox Armor costs $99.95 for iPhone 5.
edit Where to Buy
LifeProof and OtterBox can both be bought directly from the companies themselves, as well as from places like Bestbuy and Amazon, with a small discount. The official LifeProof website also offers the chance to purchase a complete guarantee against water damage.
The Amazon Best Sellers List for smartphone cases has several other options for smartphone cases.
PCMag praised LifeProof’s resilience, but claimed it made the screen duller and more reflective. They also criticized the sound quality of calls.
According to a review by News Observer, the OtterBox can withstand being driven over by a car.
LifeProof was the About.com Reader’s Choice in 2013 for Best iPhone case. It also won the Backpacker 2013 Editors’ Choice Snow Award, and was name the Best iPhone Case of 2012. It's lighter, more fashionable looking, but not as sturdy as Otterbox, although it's still 100% waterproof.
OtterBox is the number one bestselling smartphone case in the US. It's plain-looking and almost twice as heavy as LifeProof, but extremely sturdy and scratch-proof.
edit OtterBox acquires LifeProof
In May 2013, OtterBox acquired LifeProof, making it the no. 1 company for smartphone cases. While the terms of agreement are not completely known, both LifeProof and OtterBox can both be purchased at their respective websites.