See this for RCN's take.
See TiVo's site for all their pitch. (Ignore the costs on TiVo's site - you'd be renting the box and service from RCN and their pricing hasn't been set.)
TiVo is the original DVR. Everything else is just an imitation (and the courts think so too - look up TiVo vs Dish). It's faster, has better menus, can be on your home network so you can transfer shows off of it and can download movies from Amazon and Netflix On Demand, and so much more. Add the fact that the new RCN version will do VideoOnDemand. Seems like no contest