I think that the WS classes are "watch and learn" type classes, while most of those at the Chopping Block are completely hands on, ie, you actually get to cook during the class. So it would depend on which approach you were more interested in.
The Chopping Block has a pretty good reputation, but I don't know about the WS classes, sorry!
Anthony Bourdain on Barack Obama: "He's from Chicago, so he knows what good food is."