1 GB of GDDR5 is better. 2GB of DDR3 is slower overall. Faster RAM gives you better game performance, larger quantity does not always give boost your game performance. especially on lower end video cards. The 6670 is not powerful enough to use more than 1GB of RAM, that card will rarely use more than 512MB, so having 2GB of RAM will not benefit you at all with a 6670.