Bandwidth test sites try to connect you to the closest test server possible. My guess is that the Cnet test isn't connecting you to a server as close as the Speedtest.net one. Go with the Speedtest.net results.
Does anyone know why the CNET speed test indicates a much lower speed than speedtest.net? I get 2.0 mbps from CNET and about 29 mbps from speedtest.net. I know the higher number is not correct but don't know why it tests that way. My cable company doesn't take me seriously because they reccommend speedtest.net for testing.