How-to: Select Best Download Server for Ubuntu Packages
Except I recalled a feature that is in Synaptic that has been carried over to Ubuntu Software Center. Go to Edit -> Software Sources in the menu. You can also do this from the Preferences for Synaptic or the Update Manager.
Under the Ubuntu Software tab there's a drop-down next to Download from:
Selecting "Other..." will present a list of servers on the left and on the right a button that says "Select Best Server";
Just click the Select Best Server and Ubuntu will ping all download servers, run some tests to see what mirror will give the best download speed, then choose the best server automatically
Now it doesn't necessarily choose the closest server geographically, nor does this guarantee that the chosen server will always be the fasts - just the fastest on that occasion you run the test. So you may find the download speed is worse than your regular server once the peak demand is over. Keep an eye on it, don't be scared to change servers when things slow down. RC