Best for me is the Apple Bumper.
I bought a Griffin Reveal right after getting my iPhone 4 and HATED it! The plastic back scratches way too easily, and the sides don't fit that snug around the phone.
Also bought ZAGG InvisibleShields and hated those too. Wasn't a fan of the texture and orange peel effect!
When I had my i4 I would have to say the the best case was the Speck GeoMetric and the worse was the Griffin Reveal. Took some time to get use to the GeoMetric because of the uneven back, but it was cool after a while.
I actually have that hdd case too. I sure as hell don't put my phone in it but it holds my power adapter, usb cable, kingston battery backup, apple in ear headphones, 3.5mm to 3.5mm cable, a couple of microfibres, and a couple of iKleen wipes just fine.