I think they are both good, think it comes down to your tastes. I like KEFs myself but I would say listen to both and use the media (HT, audio) that you play the most
I will be interested in your impressions of the B&W 604 S3's. I am in the process of upgrading my speakers and these were on my list. I auditioned them a couple of weeks ago against the PSB 6t's. There were differences I liked about both. I felt the 604's could really handle the power and play very loudly and were quite dynamic. However, I felt the bass was really lacking at low volumes compared the PSB's. I felt the 604's were more forward than the PSB's (but not bright). Great looking speaker. I determined that I prefered the 604's to the 6t's. However, I this past weekend I auditioned the PSB Silveri's and I prefer them to the 604's. I am not familar with the KEF's though. I would be curious to your thoughts on the B&W's.