Cheapest may be best in this case.
Cards like the Hauppage PVR-150 encode video to mpeg2 -- but they introduce a delay. It's not an issue watching live TV, but if you're going to use the PC display while recording and playing the ~1000ms delay may be objectionable to you. If you're using some kind of video splitter, the hardware encoding cards cause very little CPU load and output small files to write to disk and would be your preferred solution.
Frame grabber cards will all perform about the same -- it's up to your encoding software to keep up at the resolution and frame rate you specify. You could also dump raw video to the HD and encode later.