State of the art for 3D video adapters changes more quickly than for any other PC technology. If you buy a $300 bleeding-edge 3D adapter that's the fastest on the market today, that adapter will have only midrange performance in six months, and entry-level performance within a year.
ATI and nVIDIA vie constantly for the title of world's fastest 3D adapter, one-upping each other frequently. In general, except when one or the other introduces an entirely new chipset, the fastest current ATI and nVIDIA 3D video adapters have performance within a few percent age points of each other. Which one is fastest depends on which benchmark you believe, which 3D applications and games you run, and what resolution you run them at. And the truth is that any reasonably recent ATI or nVIDIA 3D accelerator is more than fast enough for any but the most intense 3D games.
Of the two, we used to prefer nVIDIA because ATI drivers were often quite poor. In the last few years, we've come to prefer ATI overall. ATI has greatly improved its drivers, including its Linux drivers, its 3D performance matches or beats comparable nVIDIA cards, ATI 2D graphics and text are of noticeably better quality than that of nVIDIA, and ATI video capture functions are far superior to those of nVIDIA. In short, if all you want to do with a video adapter is play 3D games, it's probably a tossup between the fastest models from ATI and nVIDIA. But if you also want to use the video adapter for web browsing, email, and other typical productivity applications, we give ATI the nod for its superior display quality.
If you're building or upgrading a general-purpose system?one that will not be used for 3D games or professional graphics?we suggest you not worry much about which video adapter to choose. For undemanding 2D applications such as word processors and web browsers running at moderate resolution?in fact, for anything other than 3D graphics or other special requirements?nearly any reasonably recent embedded or standalone video adapter is sufficient. If you're buying a motherboard, buy one with embedded video if that is an option. Make sure the motherboard has an AGP slot and allows the embedded video to be disabled. That way, if your needs change later, you can install whatever video card seems best. If you're upgrading a system with an existing AGP-capable motherboard, buy an inexpensive AGP video adapter. If the existing motherboard is an older model without an AGP slot, that itself is good reason to install a motherboard that has an AGP slot and embedded video.
For our most recent detailed recommendations by brand and model, visit: http://www.hardwareguys.com/picks/video.html.