it all depends on what exactly your needs are. You will have to look at some of the differences of the cards. Personally, I would go with a PCI card.
Some cards offer dual tuners so that you can record a show on one channel, and watch another channel at the same time, or record on 2 different channels at the same time.
I will STRONGLY recommend that you get a card that has HARDWARE encoding of MPEG, as opposed to software encoding. An example is that I have an ATI All-in-wonder 9800 in my media PC, and it uses software encoding. If I am surfing the net, or doing something else that uses CPU power, and a show starts to record, the program will usually have video artifacts, or video or audio will cut out for a few seconds at a time.