I replaced my Tivo Series 2 unit when Comcast began offering dual tuner HDTV/DVR in "one box"
Here's the pros of the comcast:
1) never "messes up" changing stations (the IR blaster on the tivo would blow it every once in a while)
2) Easy to watch one channel, record another. I frequently also use the second tuner as my "digital music" source for whole-house stereo
3) HDTV recording!!!
4) $10/month covers both HDTV signals and DVR (cheaper thn $5 for HDTV plus Tivo fees of $12.95/mo.

The single biggest pro of the Tivo is that their user interface is superior.

Your call, but I've been happy with my switch. FWIW, if I didn't have HDTV, and I didn't need a cable box anyway, I would use TIVO.