If you are a cable subscriber, you do have two choices. Cable companies typically offer their own DVR service, and also typically support customer-owned DVRs, of which there is only one, currently on the market: The TiVo HD (and the premium TiVo HD XL). The TiVo is the better device, overall, with a better user interface, on average better reliability, and many advanced features not found in the typical cable company DVR. By comparison, cable companies generally do a better job supporting their own DVR, and since you rent instead of buy, if something ever goes wrong with a cable company DVR, you can get another one without too much trouble.
Note that, in most areas, there is no such thing, these days, as plug-it-in-and-go. Most cable networks are broadcast by cable companies encrypted. Therefore, you must rent some cable company equipment to receive those services. Today, that's typically a CableCARD. The typical cable company DVR has one inside it, while the cable company installs one into the TiVo HD (with fees for installation, and for monthly use of the CableCARD). Without a CableCARD, there are other limitations imposed on the TiVo HD.