i personally use tmn because it's the most accurate for me, and i like the way the site is setup with the forum, ping tools, etc. but if tmn is down (like the great crash we had) i use speakeasy, it seems the second closest.
here is a note for you shug, i never use speedtest.net because they only have 1 size speed test it seems, and if i choose a close server to test, even though i am only on a 3mbps download connection, i still lose a bunch of speed with it. so for me it is extremely inaccurate, because on dumeter(registered) i dont get close to the speed i do on tmn