How do i know what video card to get?

So i was trying to update my video card to play video games, i ran a system check at systemrequirementslab.com and found that i need a minimum of a NVIDIA GeForce 7600 GT or ATI Radeon HD 2600 Pro. I found some great deals on video cards but how do i know which is better? are the newer cards are the higher the number is?|||Best video card to get for the price right now is the 5670 from ATI.