To launch Synaptic, choose System > Administration > Synaptic Package Manager
Now you need to select Settings -> Repositories.
Select Ubuntu Software tab In the Download From drop down, choose Other...
Click the Select Best Server button in the resulting dialog.Wait a minute (or perhaps more on a slow connection).
Testing best server is in progress
Once it's finished,click on choose server
close everything and click Reload in the main Synaptic window.
Downloading package information in progress from your new mirror
This simple procedure picks the best mirror for you. This works for me very well so i would suggest you try this and see if it works for you or not.
If you have any other method which worked for you please let us know.