Click on the link in my signature line. You'll see that I have both and it's fairly easy to do an a/b compare. Since then I've moved the on-walls up a bit. I originally had them even with the middle of the TV.
The easiest way to describe them is the on walls are a bit bright, whereas the book shelf are more bassy, but even. Together I have the best of both worlds. The on-walls excell in the mids and highs, there is some bass coming out of the ports on the bottom, but not real noticable until I have the AVR set them to Large, with no lower crossover. Large is how I liked them the best. But with both types, I like it best with the cross-over set to 80, otherwise, there is too much mid bass.
