Logitec keyboard case (for iPad 2)... fits the new iPad perfectly. Love how they snap together for all-aluminum look that could pass for a laptop. Also love the smartcover (red leather) and a leather envelope slipcase I picked up @ Radio Shack.
I love different combos for different reasons: smartcover + slipcase when I can leave keyboard behind... Logitec when I need keyboard, and Logitec + smartcover (it does rest nicely if a bit less securely in the keyboard case-tray with the smartcover nestled between the keys and the glass.
The only one of mine that protects the back of the iPad is the slipcase...
Still experimenting, but I will add to rather than replace any of the ones I currently use!
I am very happy with the leather smart cover I bought with my new iPad, but it does leave it a little exposed when rattling around inside my briefcase.
So I just invested in a Targus Z-case (available here in UK for 15 or less), it adds a solid shell around the iPad when it's being transported, and is compatible with the new iPad (3rd gen) and smart cover.
Aboslute favorite case? Well I can't even find anything that even works for me yet. So I say NONE .I did love using a white hardshell Incase snap with smart cover on my iPad 2. I am looking for something like that.
I'm very happy with my RooCase Convertible. I love all of the different reading angles and the magnets work perfectly to turn the iPad on and off. I wish it didn't hide the bezel, and I wish it was a little lighter, but I can't find anything that's absolutely "perfect" so this will do just fine for now.
Just ordered a Pad and Quill case. I have 2 already - one for a Kindle Touch, one for a Fire. They are top notch USA made hand crafted by a book bindery. For $60 its a steal considering the quality and US make.
I have a Cygnett bubble case I got at RadioShack for $15 which I use when I take my iPad away from home. But Ghost Armor on front and back and light blue smart cover for home. But would really like to get my hands on this one...