How do I tell what my download and upload speeds really are?

How do I tell what my download and upload speeds really are? Charter Communications is my ISP (not by choice, all that’s available here) where I’m paying for 18 Mbps service, Charter has two different test site and the results are not even close between them.

At (wired) http://spt01sfflva.sffl.va.charter.com/ I get a download speed of 8.2 Mbps and upload speed of 1.9 Mbps.

At (wireless)  http://spt01sfflva.sffl.va.charter.com/ I get a download speed of 3.9 Mbps and upload speed of 1.9 Mbps.


At (wired) http://spt01spbgsc.spbg.sc.charter.com/  I get a download speed of 20.8 Mbps and upload speed of 1.9 Mbps.

At (wireless) http://spt01spbgsc.spbg.sc.charter.com/  I get a download speed of 9.4 Mbps and upload speed of 1.9 Mbps.

This one is totally bogus:
At (wired) http://www.speedtest.net/ I get a download speed of 40.12 Mbps and upload speed of 1.8 Mbps.

At (wireless) http://www.speedtest.net/ I get a download speed of 7.49 Mbps and upload speed of 1.8 Mbps.

Phil