Mine is the Defender by Otterbox. I love this case because it means that I don't have to carry insurance on my phone because if I drop my phone I know it's covered. Sure I probably should still have insurance but I like living on the edge. Some people say that putting the iPhone4/4S in a Otterbox is like putting a supermodel in sweatpants, but I would rather have my phone be bulky and protected.
OtterBox is my most-used case company by far. I use to use the Defender series on my iPhone 3G and iPhone 4, but now I've been using the Commuter case, it's a bit smaller, and thinner, but the protection is great.
And I thought the iPhone 4 was the greatest thing I've ever bought. But I must say the lifeproof case is just as equal to the iPhone 4. That makes my life twice as nice. Specially having kids that love watching netflix on my phone... lost already couple of them ... So, Lifeproof is the best... and is water proof... can beat that !!
It has to be the Seidio Convert case.
I can have the surface case for everyday and put on the rugged portion for when I am on the firetruck or ambulance.
speck.. (candyshell).. the rubber on the inside and plastic on the outside.. the rubber protects it from when it falls and the plastic makes sure the rubber doesnt stretch out like how most other rubber cases do and protects the back of the iphone from scratches..
Of all the cases that I've used for cell phones over the past seven years, Seidio is probably my favorite brand name thus far. Not only are they sturdy, but they can take a serious beating. I was quite pleased with the reliability of the Convert Value Pack for my iPhone. Never had to worry about breaking my iPhone while it was protected in that case and holster.
The latest one I have is the Case + Holster combo for my Samsung Epic 4G. The case keeps a vicious grip on my phone even after swapping the battery and back cover for the 3500mA battery and extended back cover.
There have been times when both have been knocked off of my belt while working in the warehouse (coming around a corner while carrying something large and it catches a box on a nearby shelf), but the case has protected my phone in these circumstances.
Convenience and reliability make Seidio my favorite.