I have the Candyshell for iPhone 4. I've had it for about a month. It's nice, much the same as the iPhone 3G version. The hole for the flash is too small so it causes the flash to blind the camera a little. This is something Speck is fixing and that's why there's a delay. Speck has said they'll replace my case when the new one is out.
The other thing is the rubber is totally peeling on my Candyshell. It's barely a month old and the rubber area around the front bezel of the screen is totally peeling & fraying. It's really really bad. I'm sure Speck will replace it, but it does concern me that this will always be an issue with this case.
I just ordered an incase slider. I'm not happy with the lack of detail their online photos offer, so I hope there's a money back guarantee. For instance I have no idea how big the dock connector hole is at the bottom and if it'll fit after-market iPhone dock cables which are usually a little larger than the OEM Apple ones. Also, some cases wrap around to the front of the screen and interfere with screen protectors (iFrogz has this issue) I'm not sure if this will have that problem. We'll see once I get the slider which will be in about a week I hope.
Once nice thing about incase is that they have a "Integrated glare reduction ring in camera cutout." It's a matte black ring in the camera/flash cut out there specially to reduce flash issues. This is a nice feature.
There's also a "Stand included for upright viewing of widescreen." I guess that's just a little plastic stand? I guess it'll be handy on rare occasions.
I've also got my eye on the Otterbox Commuter (not the defender, too bulky.) The commuter looks pretty thick too, but I might like it. It depends how much I like the icase whether or not I'll try the otterbox.