Why don't you listen to both of them for yourself and be your own judge? Lots of folks like B&W, and VS has a loyal following as well. So obviously both vendors must be doing somethig right, for at least some segment of the listening public. Also, you haven't said anything about your equipment or what types of music you listen to.
Having said that, if I had to close my eyes and choose I would probably lean towards Von Schweikert. I have owned both B&W (Matrix and Nautilus) speakers, and had a pair of VS2s for about six months while a friend was travelling. The B&Ws were both very good, if unexciting. The Von Schweikerts are much more lively, musical and fast IMHO. And, properly placed, they image like the dickens.
But why just these two brands? Based on your requirements (and again, not knowing anything about your system) I might suggest that you listen to one of the French speaker lines: Focal, Triangle or (my favorite) JM Reynaud. Not to over generalize, but I have found that all of these brands tend to lean towards warm, detailed, forgiving and great imaging. While Iwouldn't decribe any of them as analytical, the some of the Focals are more so than the Traingle than JMR. I have a pair of Triangle Cometes in my den and enjoy them very much. I just bought a pair of JMR Offrandes (on A'gon) and am looking forward to setting them up in my new listening room, which is a converted 3rd garage stall about the same dimensions as your basement.