Believe it or not, Comcast was a MAJOR upgrade from AT&T for me.
I used to have the @Home cable modem service and was quite pleased with it. This is before the days of Doxis and there was no throttling. My cable modem was capable of 10Mbps up and 10Mbps down. Later, @Home reduced it to 10Mbps down and 1Mbps up. Times were still good since that was an insane amount of bandwidth.
Then AT&T bought out @Home and switched it to AT&T Broadband Internet (ATTBI). They decided to reduce the upstream bandwidth to 128Kbps, but they aggregated all of the users through the SAME 128Kbps pipe. As a result, on the best of days I saw 40% packet loss with ping. My old 28.8Kbps modem was faster than my cable modem. It was like this for 9 months. Technical support was absolutely useless. There were newspaper articles about it but still the incompetence continued.
When Comcast took over things improved drastically. I will go out of my way to avoid anything to do with AT&T. While Comcast has a lot of problems, it is nothing like what I experienced with AT&T. AT&T was absolute shit.