I have heard both
but not side by side. Where I live, there are lots of Cambridge Soundworks. I own a pair of the M-60s and I have listened to the M-80s on many occasions. They are a good clear sounding bookshelf speaker with surprisingly low bass for a bookshelf. Moreover, the low bass rolls off nicely, and these would work well with a subwoofer. They are also fairly good at imaging.
I listned to a pair of Bower and Wilkins 602 S3 bookshelf speakers at Spearit Sound in Framingham, MA. Again I was impressed at how clear these sounded. They had great imaging, and when set up on stands, WOW. Again surprisingly low bass for a bookshelf, but would probably sound best with a subwoofer.
I can't tell you which sounded better because I didn't make an AB comparison, but I was impressed with both when I listened. For "Cache" factor, I would go with the B&Ws. Otherwise I wish I could line up a swithbox and compare B&Ws, Polk Audio LSi9s, Dali Bookshelves, and the CSW M80s and just listen to each.
I think if I had to choose, I would go with the B&Ws, I remember being slightly more wowed with their performance for a bookshelf than the CSWs. However, I've long been a fan of CSW, and I still love my M-60s. Really the best thing for you to do is find a store and listen.