The word is that the ATI looks and sounds better.
The one day(!) I got it to play a picture without locking up, I could not see any difference. (radeon VE, DILA)
I never could get it to play sound, even with DVD Genie, and unregistering WinDVD. So either it sucks or I suck, but I'm too busy watching movies to worry about it.
The neat thing about WinDVD is that it works, and passes DD and DTS without much fuss.
YMMV,