No doubt, CPU is the brain of the computer. But when we talk  about the games, the graphic card or video card is the beating heart that pumps pixels out of your obelisk of a tower and into your monitor. A graphic card consists of dedicated video memory and a graphic processing unit that handles all sorts of calculations, like mapping textures and rendering millions of polygons. Simply, the graphic card is the most vital component of your gaming PC.
Games are rarely handled by your CPU, but dozens of games every year will push you graphics card to its limits. It's the component you'll want to upgrade most frequently (though if you buy the right card, it should last you at least two years), and likely part you'll spend the most money on. On a practical budget, it;s critical to find the graphics card with the best ratio of price to performance. That's why my recommendation for the best graphics card is the Nvidia GeForce GTX 970.

Nvidia GTX 970 is the best card, I would recommend to most of the gamers, but not to all. 
May be someone got cash to burn, and wants to run games at 4k resolution. Or maybe, you are as same as me :P. I mean some of you, may be trying to built a PC at low budget. There are a lot of different cards with all kind of ranges. 

Nvidia GTX 970 looks something like this:
Nvidia GTX 970 

Testing Graphics Cards

Our graphics card recommendations are based on our own benchmarks and testing, as well as research into the reviews and testing done by other sites. Along with Maximum PC, we have benchmark data for a range of Nvidia and AMD graphics cards, including the GTX 980, Nvidia 700 series, AMD R9 290X, and more.
What makes the best graphics card? For PC gamers, it's a balance of price and performance. The graphics card must be able to run demanding games at high framerates and settings at 1080p, the resolution most gamers still use. It shouldn't cost more than other cards with comparable performance. The card should be fast enough to still perform respectably two years later, even if it can't run everything at max settings.
Graphics performance isn't the only consideration. The quality of game drivers and other software features supported by the card are important. The card's noise level, power draw and temperature matter, too.
Quoted form: PCGamers