Let's face it: Most people who buy a video card (also known as a graphics card) for a non-business PC are doing it for the purpose of playing games. Oh sure, discrete video cards may confer additional benefits with video playback or transcoding (and, increasingly, Web browsing), but who are we fooling? The main reason discrete video remains such a huge and fiercely competitive market is because, when it comes to playing games that don't come from casual-oriented companies like PopCap or Big Fish, games with major titles like Mass Effect 3, Batman: Arkham City, or The Elder Scrolls V: Skyrim, integrated graphics—even of the drastically improved varieties you find on the latest CPUs from AMD and Intel—just don't cut it.

The ugly truth about buying a discrete card can essentially be summed up in five sad words: The more expensive, the better. There's almost no way around the fact that the more money you're willing to drop on a video card, the better your gaming experience will be. If you can spend $500 (or more—and yes, that is possible), you're going to be buying yourself an outstanding gaming experience, even if the rest of your computer isn't so special.

That said, there are a few additional things you'll want to keep in mind when selecting a video card. They're all subsidiary to that one (sorry), but may help you make a better determination if you don't want to buy a lone card for the same amount of money you could otherwise pay for a complete computer system.

AMD or Nvidia?
Would you believe that this question just doesn't matter that much? I didn't think so. Like "AMD or Intel?", "Windows or Mac?", and "Desktop or laptop?", it's a question that inspires intense—and often nonsensical—debate among each side's adherents. We're not going to lie to you: There are substantial differences in the technologies in AMD's and Nvidia's graphics chipsets, and if you're really picky, you may have a very good reason for choosing one over the other. (We'll touch on this later.)

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The truth, however, is that only serious, detail-obsessed gamers are going to be able to discern a difference in appearance between a game running on an AMD card and one running on a comparable product from Nvidia. Most people are going to pay more attention to how realistic a game looks and whether it stutters during play than the specific types of anti-aliasing, physics processing, and multimonitor technologies that are employed. If you find a card at a price you can afford, and reviews say it does well, go with it. Most of the other stuff is just gravy—and often lumpy at that. (Note: Several years ago, AMD bought and absorbed video card maker ATI. All AMD's cards now carry AMD branding, but 5000-series and earlier models may still have ATI emblazoned on them somewhere.)

GPU
A video card's graphics processing unit (GPU) is what determines its video capabilities, and many GPUs have names that are often fairly arcane and unintuitive if you don't follow the business closely. But a good rule of thumb is that the higher the number in the GPU's name, the more recent and more powerful it is. For example, in Nvidia's newest 600 series, the top-of-the-line (and most expensive) card is the GeForce GTX 690.  If you want something more affordable, but still unquestionably powerful, go for a GTX 680 or a GTX 670.  On the other hand, the strongest card in AMD's current generation is the Radeon HD 7970, followed closely by the 7950, the 7870, the 7850, and so on down.  But the company's most powerful card is, as of this writing, the 6990, which was unleashed in 2011.  That's the only significant exception at this point:  Otherwise, within each company's catalog, a card with a higher number in its name is invariably a superior performer.

Memory and Clock Speed
Ultimately, video cards aren't much different from CPUs—a lot of the same rules apply, including those about memory and clock speed. Video cards have their own collections of both, although the specific values of either will usually be less immediately important than when you're choosing a system processor.  It's possible for two video cards of the same type to have different amounts of memory—the GTX 580, Nvidia's single-GPU flagship from the last generation, is available with both 1.5GB and 3GB of memory—and the one with more memory will tend to be faster and cost more. Likewise, some cards might use GDDR5 memory, which is faster and more expensive than the DDR3 and GDDR3 memory other cards use. Lower-end video cards sometimes have faster clock speeds to compensate for the power they lack in other areas, but that's usually not going to translate to increased real-world performance. You only need to pay close attention to these specs if you want to fine-tune your purchase; in most cases, the name of the GPU will tell you everything you need to know about the card's capabilities.

Length
Back when all computers were two-foot-tall towers, no one thought much about video cards hogging a lot of space. But because PCs now come in a range of sizes, you may not be able to use every card in every system you want to build. The more powerful a card, the longer it's going to be, and the less likely it will fit into a microATX case, or even a smaller ATX case. At 12.5 inches, the aforementioned Radeon HD 6990 is the longest card you can buy, but some higher-end AMD and Nvidia cards come within an inch of that. If you're building a smaller computer, or you want to upgrade the video in a minitower you already have, be aware that your card choices may be limited.

DirectX
Video cards will support different versions of Microsoft's DirectX collection of advanced programming interfaces (APIs), which offer different graphical and processing features. Again, the specific details are going to be important only to hard-core gamers, but the higher the version number of DirectX a card supports, the more realistic games that use it will look—and the more challenging they will be for your computer to run. The highest-level version as of spring 2012 is DirectX 11 (DX11), and cards that can run it will also be able to run the full feature sets of games written with DX10 or DX9, but DX9 or DX10 hardware won't be able to see all the effects of DX11 games (assuming they work at all). The software package or the manufacturer's website will tell you what version of DirectX is supported—always check to make sure your hardware matches up. All the latest AMD and Nvidia cards support DX11, so if you buy new you won't have a problem.