QOS tests & Service Providers

I have AsteriskNow setup and have tested internally with softphones. Works just fine. I have done several of the online VoIP tests and get mixed results. I have Comcast cable and get good d/l and u/l speeds but poor on the latency and QoS on some of the tests.

How accurate are these?

How much does the service provider play in this?

Anyone want to comment on VoIP Your Life or Packet8?