I don't know what RPTV does that Tivo doesn't.
Tivo is fun because it fills up otherwise unused space in its spare time with "suggestions," TV shows and movies that you might like. The thing is, you can't get crazy with the "Thumbs Down" button, otherwise it eventually thinks you don't like anything at all and so it won't have anything to suggest. If you use the "Thumbs Up" button a lot, you'll never be without something to watch. When I first got the Tivo, I started pressing thumbs down to any show I didn't like, and within a couple weeks, it wouldn't record anything other than what I asked for. So I reset all the thumbs ratings. I thumbs-upped all the shows I did like, and I only thumbs-downed "Paid Programming." I just ignored all the shows I didn't like and they deleted themselves automatically whenever it needed more space. It started recording some good suggestions for a change, and as I thumbs-upped more of the stuff I liked, it got better and better. I'm never without something to watch, even though I recently dropped almost all of my cable TV channels, relying only on the few channels I get for free as a Road Runner subscriber.
RPTV doesn't have a monthly fee though. Tivo does, but you can put a unit on a lifetime plan for some large amount of money. I might upgrade to a permanent subscription but that takes like three years to start paying off.
Overall, I think my Tivo rocks, but I don't like the $12.95 monthly service fee. The original series Tivos can be upgraded with a $99 card so you can plug it directly into a router, rather than a phone line. I think the series 2 Tivos have that functionality built in.