What is Your Favorite iPhone 4/4s Case?

I currently have a glass sandwich in need of protection, and would like some opinions on cases. Because the designs been around for a while now, there are so many to choose from, and, probably, heaps of rubbish ones too. I like the look of the Book Book, but also looked at some battery cases, most notably the 'Incipio OffGrid Pro'.

Bookbookiphonecase20110115_medium

What are your thoughts?