This mirror is:
barney.w3.org 128.30.52.38
You may or may not get the same mirror on each request, depending on how your browser handles multiple IPs for a hostname. Reloading this page a few times should let you know if your browser is connecting to the same mirror each time.
Mirrors currently in service for www.w3.org:
128.30.52.166 128.30.52.168 128.30.52.170 128.30.52.38 128.30.52.51 128.30.52.53 128.30.52.54