I have the Apple case and keep it in my messenger bag or backpack as I'm out and about. I like the Apple case because its thin and works as a multiposition stand. The thin profile lets me get lots of other stuff in the bag.
I agree. I have tried a number of cases, based on some negative comments about the Apple case.
First, I tried the Yoobao V2 (bonded) leather case. It's heavy for what it is, and doesn't double back flat, so is annoying to hold. The iPad also tends to slip down (despite the flap holding it in) when placed upright. It is also quite bulky.
Secondly, I tried (and still have, for more adventurous outings), the Otterbox Defender. It offers great protection, but not only does it weigh a tonne and is very thick with the cover on, it has left some marks on the rear of the iPad. Mine never exhibited the "oil slick" pressure problem unless I deliberately applied pressure.
Third was a cheap eBay flip case with magnets holding it in place when folded back, but it was flimsy and started to wear even after less than a week. I gave it to my mum.
Then I just went out and bought the Apple case Saturday last. It is great, offering good protection, even to minor impact, as the edges which some feel are sharp (they are not) can absorb some shock. Its rubbery feel makes it easy to grip, it will accept the photo adaptor, it is light, and it is nice and thin, to slip into my MacBook bag (a 13 inch STM Scout messenger-style bag).
I don't think I'll use the Yoobao case, just the Apple case and the Otterbox for army deployments or exercises.