I have Cox Roadrunner service, and I have to say that the Customer Service Reps that I've dealt with have been nothing but pleasant and helpful. Their Tier 3 tech support is virtually impossible to get in touch with, but besides that, I have had a very positive experience in dealing with them. I did have a severe sporadic problem with the overall speeds on my connection. Some days I would get 1.3Mbit/sec, some days I would get 28.8Kbps (I really mean 28.8 ... I was getting 2-3k/s downloads!), and some days I would get a dead connection (modem would lock a downstream channel, but would never synch). Anyways, CSR had a lot of trouble tracking down my problem, and in the end they finally figured out that it was an extremely bad signal to noise ratio on the router I was using (I'm not exactly sure what that means since I dont have any experience using cable equipment but I'm assuming that the quality of my connection varied based on how many other people were connected at the time, and as more people connected, the Signal to noise ratio dropped so low that I was getting horrible packet loss, or no connection at all!) The past week I've been on at 1.3Mbps with no problems though so *knocks on wood* hopefully it will stay that way.
Might want to just try asking them to check out the routers in your area and see if that might be the problem.
Personally, dealing with Cox Roadrunner CSR's has been A LOT better than dealing with Comcast@Home CSR's and now from what my parents tell me Comcast.Net's CSR's are even worse!!!