Which Environment Variable should I choose?

Hi Friends

I want to put my server name in the environment variable to make my package dynamic.

All my packages will be run & scheduled by my DBA from his computer.

So when choosing the Envirnoment Variable which one should I choose in My Computert Properties: User environment  variables or System environment  Variables?

Also please specify difference between User environment  variables and System environment Variables and their purpose.

Royal Thomas