I auditioned both when shopping for speakers about a year ago. As I recall, both sounded very nice. The B&W's seemed to have a little more bottom end and sounded a little fuller. The JMLab's were a little lighter on the bottom but with excellent mids and very detailed highs. Had I chosen between them, I probably would've gone with the JMLabs. I ended up with Paradigm Studio 20's which, to my ears, combined the best qualities of each of the two you're looking at.
That said, I will tell you that I did not audition any of the above mentioned speakers at the same time or in the same store. Given that the listening environment greatly affects what one hears, it's quite possible that my perceptions of these speakers is not as fair, equitable and accurate as had I auditioned them in my home at the same time.