The TiVo makes it so easy to find and record programs that it's worth the $10/month, IMO.
Alternatively you can buy the $300 so-called "lifetime" service from TiVo. It's for the lifetime of the TiVo box, which might be short or long depending on the hard drive (I think most failures are hard drive-related).
Personally, I'd do the monthly. This industry is changing rapidly and 30 months is a long time.
Buy a low-capacity TiVo, sign up for the monthly, see if you like it, then wait for a deal on hard drives and send drives and TiVo to
www.weakness.com or similar to be upgraded. I started with an 80 GB, now have a 320 GB.
I don't have any experience with cable company DVRs or with HD TV.