If I want to have the best performance what shold I set my port to?
You should leave them at default, but they are of no effect if you don't set up the Port Forwarding for them. To setup Port Forwarding, leave the GunZ ports at 7700 ~ 7800.
Then, go to this site and navigate yourself to your Modem, then Program (GunZ Online).
You should then RESTART your modem, allowing changes to take effect.