I have Mediacom in Iowa City, and it's terrible. When I was paying for the 10Mbps service, I'd generally get around 2-4Mbps down, and maybe 200kbps up. I called them and changed my plan to the 3Mbps service, and now I still get about 2-3Mbps down, and 200kbps up.
However, I'm planning on switching to Qwest's 12Mbps DSL now that they've finally gotten around to wiring my neighborhood with fiber. I had Qwest at my old house and it was great. I had the 3Mbps service, and reliably got 3-4Mbps. Cable download speeds are too erratic for me. Also, Qwest gives you 1Mbps upload, which is nice if you're uploading lots of pictures or anything like that. I consistently got 1-1.5Mbps upload out of my DSL.
Also, from my personal experience, Qwest's customer service is much better than Mediacom. I'm tired of having to reset my cable modem once a week when my Mediacom VoIP decides to stop working. The "legacy" telecom phone system may be old and out-dated, but the thing just works, as it has for years. Mediacom has a long way to go before they can say they provide a "reliable" phone service.