To find the fastest mirror in Debian, download and install apt-spy.
apt-get install apt-spy
Apt-spy is a program used to test a series of Debian's mirrors for bandwidth. Apt-spy will then generate a /etc/apt/sources.list file with the fasted server. You can select which of the Debian server's to benchmark by geographical location.
Run this command to retrieve the latest list of Debian mirrors
apt-spy update
To find the fastest mirror, run
apt-spy -d stable -a ALL
or