I've used the BT878 chipset (same one as the lower quality leadtek ones use, the XP and the XP deluxe. The higher end XP Expert uses the same Cognexant chip as the Asus), as and currently have this Asus TV880 card. The Asus card is definitely better, no 2 ways about it.
A few days ago, I got dScaler (v4.1.6) working with the Asus card, and the quality is amazing. If you have one of these Asus cards, you really owe it to yourself to give dScaler a try for TV watching.
I also bought one of the new Philips SA chipset cards (the Flyvideo 3000 TV/FM, 9-bit SAA7133 chip). I haven't gotten this to work with my 7505 chipset mobo yet, but from what I hear, the Cognexant 10-bit chip has a bit more resolution, but it also has a bit more noise in the picture. Color shift is about the same between the two.