For all intents and purposes, its better in the long run to rent your modem, at least from my experience. Friend of mine bought his own, while i rent mine, I get beaucoup support from the cable company if i have any issues with my connection, if you buy your own they always blame everything on your private modem (That was his issue, he ended up selling the modem and renting one). Thats generally the way it is with most cable companies, unless comcast isn't the antichrist like Adelphia is here.