Comment Filesharing sites (Score 1) 294
I've found the best speedtest solution is to choose a couple of the major fileshare sites (ie. the ones that ISPs love to throttle or block). I then upload a non-compressible junk file of about 100MB and try downloading it directly and via a VPN. I then compare those results to my ISP's speedtest.
I've seen some impressive throttling or within-ISP network congestion/lack of interconnects.