Some of the earlier nvidia "nforce" chipsets had some funky issues, but I think most are reliable in linux at this point.
All in all, it's been my experience that Intel chipsets are hard to beat. They run on everything.
I run a MythTV server+frontend and a separate backend at the house. You definitely will want an nvidia-based card if you plan on using xvmc etc. with MythTV for the smoothest playback... Even still, an FX5200 is more than enough for SDTV--and it doesn't generate an excessive amount of heat (unlike a monster gaming card).
The Happauge PVR-150 cards emit way more heat than I'd imagined; I have three in my backend+frontend box and had to put a dual 120mm CardCooler on them to prevent the rest of the case (mid-tower CoolerMaster) from melting