"best" case entirely depends on the user's preferences, where the iPad is going to be used, and how it's going to be used.
I own 3 iPad cases. The one I use the most is Contour's iSee case (34.95 @ the Apple store), as I am using mostly indoors with light traveling. For extended trips, I use Apple's case, since the flap for screen protection and built in stand function are essential on the go. The 3rd case I have is the Incase Convertible .. Seldom used, but my iPad with the Contour case fit inside the Incase Convertible. Gives me the quick extra travel protection I need in case I just want to slip the Contour'ed cased iPad in and go.
I have a Bluetooth keyboard that I can pair up as needed, but interestingly, I've gotten quite used to using the onscreen keyboard, and use it almost exclusively now.
If I were to purchase a keyboard case, however, the ClamCase piques my interest, as it is very "laptop-like" in appearance. I actually tried to buy one right after Christmas, but they were sold out. I checked again the other day, and the website says that they are still sold out. Was $99 with the gift card promo, but is reported to go up to $119 or more.
The other one that looked pretty good to me was the Cruxcase360, although I haven't seen any reviews on it, nor do I know if they are shipping yet. Probably just as well, since they are asking a cool $150 for the Cruxcase360. Great looking case though, I'll give them that.
I think that the Zagg case is a good choice for minimal size and weight. For the same dough, I like the Clamcase's feature/functions better, but with no official reviews or any in stock to purchase at the moment, the Zagg seems to be the best choice for keyboard cases under $100 that I've seen so far.