Actually from what I've been reading the Ati cards have some of the worst picture quality on the tv tuner, though their capture features are about the best. Cards with the Brooktree chipset usually have some of the best Tv quality, I have an Antec Tv-tuner with a Brooktree chipset, though I believe Pinnacle and WinTv also use this chipset.
From what I've heard the 3dfx Tv200 is about the best out there right overall now, too bad about the driver situation, though if you can find one for a good price it might be worth it.