I've been an nVidia fan most of my geek life but on a recent build got an ATI and am very pleased. It seems they are like a pendulum swinging back and forth between the two companies.
I agree about the CUDA comment as more new programs seem to support it. Some of the mid to upper ATI boards come with AVIVO which uses the ATI Stream and it encodes 25% or more faster for me. I do think more programs support CUDA than Stream at this point.
I may be building a HTPC soon and have no idea at this point, what I want. The good thing is that we have so many choices and the prices are very good now. They won't stay that way forever.
Custom ASUS P8Z77 V-Deluxe, Core i7 3770k, 16 GB Memory-ASUS ENGTX560 DCII TOP/2DI/1GD5 GeForce GTX 560, H80i Cooler, 750W PS, CM HAF XM RC-922XM-KKN1 case,Corsair GS CSSD-F240GBGS-BK 2.5" 240GB SATA III SSD, InfiniTV4 & HDHomerun Tuners- running Windows 8 (and other goodies)
#2--P877WS- Core i7 3770k, 16GB Memory-GeForce GTX 650Ti, SATA III SSD, H100i cooler, 750W PS, Windows 8.1