There's a standard test called HQV that rates video cards for their picture quality and video post-processing. The higher the score the better.
As a good example, this review
has both DVD and blu-ray HQV tables comparing various video cards.
As you can see from that review, the Radeon HD55xx series and higher score the best on the HQV benchmark test for both DVD and blu-ray playback.
Hope this helps.