I don't know about the new B-class model, but I recently drove the new A-class... and it was terrible. Very dissapointing. Nothing like a C-class. And the A was down right scarry in the snow. I could hardly believe it was a FWD car. My 135i with snows ate it alive in deep snow.
I think a nice Golf VI just kills the MB is design and performance. But I still would not give up my BMW to any VAG product.
The main thing that turns me off with the A and B class is their van like - seating position. The 1er coupe is a sports car. That is something you can not say of the BM products listed above.