I did some research on this myself and almost a year ago I decided to go with DVICO. They offer a few options in HDTV tuners including USB HDTV tuners (which I own) and work pretty well.
Unlike the ATI which has only NTSC/ATSC tuners. The DVICO has a QAM tuner in addition to NTSC/ATSC which was EXTREMELY appealing to me. Now I dont need an antenna to receive local HD. AWESOME.
The downside is, is that its single coax but not a HUGE deal. Because DVICO's software supports multi tuners for PIP and dual recording. The only problems I have with DVICO's software is with Vista. I cannot, CANNOT, get timeslip to work properly with Vista. Its a great feature NOT to have but a small flaw to have HD. On XP I rarely had a problem with it.
I've used ATI tuners in the Past and I thought they were the biggest peice of crap.
DVICO is a bit more expensive than most but I think its well worth the money for stunning picture in HD that rarely skips a beat.
My rating
XP: 5/5
Vista: 4/5