What a great dilemma! Both are great speakers! I think the real answer is you need to audition both with a couple of your favorite movies and also think about your room. But with that said: for mostly home theater use, I might give the nod to B&W for the extra detail--as long as you have a good sub.
Here's the longer response to your question and my reasoning: Today I have B&W 703s and CM series in use as part of a 7.1 home theater and Cremona Ms in a separate 2 channel rig. I probably spend 60-70% of my time listening to music in the living room vs. movies in the family room / theater.
I started with B&W 703s used them for both music and movies even though it was only part of a two channel system. At times I thought they were a little fatiguing but I'm sure a lot of that was the reflections from the plaster walls in my old house. I say this because when I moved to a newer house with drywall and more of an open floorplan I thought they sounded better (softer). But I still thought they were a little bright and did change my integrated amplifier and cabling. (flame suit on) I liked the differences in the 703's sound even more. Subtle differences, but they were there IMHO. And even though my system was still 2 channel, I thought the B&Ws especially shined when I was watching a movie on blu ray. The detail of the speakers are great for that.
Fast forward a little and I was starting to get the urge to upgrade. So when the B&W diamonds first came out, I went to audition them thinking I would be stepping up from my 703s. I listened to the complete 800 series, but the diamonds didn't do it for me--very accurate but not the bass I was really looking for. (again personal preferences on sound) However, in the same showroom were Cremona Ms. It took about 1/2 a song for me to hear the difference and know the Fabers were a good choice for me. There's a bit more depth in the bass and a warmer sound, which I prefer. I bought them and 2+ years later, I'm still very happy. As an alternative, I probably could have added a nice sub to the diamonds. But space didn't allow at the time.
So while basking in bliss of Cremonas, the question was what to do with the 703s which were in storage. Like I said, I thought they were great in home theater use. Plus I had a long term goal of building a surround sound system in the family room. So after my demo, I had decided that what the 703s really needed was a subwoofer. And it was a good addition. However, by the time I was ready to do more, the 700 series was long gone and the CMs were out. So I bought a CMC2 center and 2 pairs of CM5s to provide surround. It's a little mix-n-match, but I think it all pairs pretty well and I'm very pleased with the results. This is all powered by a Denon 4520.
My GF/now fiance has been through all of this with me. While she thinks I'm a little obsessive
, she does hear the differences between the two systems. She prefers the B&Ws for HT.
So how do I bring this all back to your original question: If I was only going to have one system, with the majority of my listening music, I'd build it around the Cremonas. (Of course that means I'd need the matching Cremona Center and eventually Auditor or Elipsa surrounds.
) But if the majority of my listening was movies, I'd probably go B&W and add a 2nd sub.
So trust your own ears and happy shopping!!