Assuming it is your own system you are checking, and assuming there are no bugs in the testing program, the highest numbers are the ones to believe. Because they show what your setup is capable of, if you're testing with the best back end architecture and the conditions on the Internet are right.
Having said that, when the TBolt first emerged, the speeds were so fast that the tried and true Speedtest.net was not accurate. It would show accurate download speeds but wildly exaggerated upload speeds (i.e. 60mpbs upload). The problem had something to do with frame-rate or frame-size or something, I forget. The devs fixed it pretty quick and put a new accurate version of Speedtest.net out on the Market. That is the Speedtest.net we have now and it is accurate.
I don't know anything about Speakeasy's accuracy.
It also depends on the server you use for the test. You can select different servers and get different speeds. Normally you believe the fastest. Don't get me wrong, they are all "true", but some are better than others at different times and in different places.
Lots of variables...
-Frank