I'm just going to throw a monkey wrench in the mix. I prefer monopole surrounds
I listen to a lot of multichannel SACDs, DVD-As and DTS-CDs. Trying many configurations, I always found that monopoles worked the best and with proper placement can give the same diffused sound for movies while still providing precise enough location for music. That said, you need to have the ability to properly place them, and that placement is behind and to the side the listener, not along side like bi- or d-poles and for me this is only in reference to a 5.1 setup.
I sat in a room with well over a $100K Aerial system using bipole surrounds, treated room, heavy duty gear and I still did not feel the bipole surrounds were to my liking, but that's a personal preference.