I have those designer cases too but I got an otter box because they're more protective. I broke my iPod even though it had a case
I have the OtterBox Defender. It has great protection as well as a great built in screen protecter. As for the bulk I really don't mind it, the bulk is very managble for me, and as long as it protects my phone it's even better.
I have: Two Star Fleet Academy cases, white and black, and silver and black. A Green Lantern case. A leather case. Yup. I change between the Star Fleet and GL cases.
I have a black textured case, a blackish rubber case, another black case with some kinda clear designs, a white Ed hardy lookin case, and on my phone now is the case that i bought for the powermat charger