I've been using MythTv for years; back in the analog video days, Nvidia was the vendor of choice because of they supported the linux platform (or at least, that's what I understood). Others might work, but if you wanted to avoid problems, use Nvidia. Now that TV's have HDMI, does it matter any more?

PS - I looked through the pinned hardware profiles...it looks like people are using all sorts of vendors, including integrated video on motherboards.