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Depends on what you need.
I need a case with very high level of drop protection. Getting in and out of a FreightShaker all day, my simple Incipio NGP just didn't offer the kind of protection I'd feel comfortable about. (I really like the simple good looks of that case on my wife's iPhone though)
OtterBox Defender for me.
Tons of drop protection, recessed opening around the camera to prevent scratching to lens, built in screen protector that doesn't watermark (like the 3G/3GS version I tried some months ago), and it is anti-glare without being more that very slightly grainy.
As I said before, my wife's got the Incipio NGP matte (semi-clear). It is ultra simple, fits very nicely (headphone cutout is very slightly off-center), and has a soft-grip feel. Fits the SGP Crystal shield well. If I didn't drive a truck, that's probably the case I'd still be using (I had the black matte)