These cases are quite different from each other.
Price aside, it comes down to whether you need an external physical keyboard built into your case.
If the answer is yes, you can choose from a number of cases from $40 on up with keyboards built in. You get what what you pay for, more or less, so a 40.00 keyboard cases are vinyl with rubber keys, while 99.00 gets you a very well made Zagg or Clamcase.
If you'd rather have your keyboard separate, you can get Apple's wireless keyboard for 69.00. Add that to Apple's case 39.00, and you're in about 108.00.
In the end you get combined or separate functionality for about the same moolah, unless of course you're undecided on the need for a physical keyboard part.. If that's the case (no pun intended), then I would opt for any case that you like and add a bluetooth keyboard anytime you feel the need to.