What is the different of series of the video card???

What are your computer specs?
What are the computers used for? internet or gaming

^ agreed.
Remember to include monitor resolution, budget and psu spec for an accurate answer.

Welcome to the forums!

As with the above, you really need to post more information.

*Are you buying these machines new or upgrading existing machines.
*What are the specifications on the machines you are buying/upgrading (CPU, RAM, PSU, etc.).
*How many machines are you working with.
*What is your budget.
*What games are going to be played and at what resolution.
*How long do you intend to use these machines for (ie. do they need to be overspeced to run future games).