It should be the same if they are not lying about there upload and download speed. For example, a 6mbps Comcast is as fast as a 6mbps DSL.
I had the 3mbps Comcast Cable Internet before and now with a 1.5mbps AT&T DSL. I didn't experienced problem with streaming videos with AT&T. Lots of factors would affect speed, basically its the traffic..so even if you are in a lightspeed connection if servers are busy then you will have same download speed as the others.
2 years ago, lots of reports regarding Comcast Throttling download speed in which I personally experienced such by the abnormal behavior of my torrents.
http://www.downloadsquad.com/2008/01/08/…
Also, DSL technology like AT&T are more upgradeable unlike cable,,,more subscribers in DSL because it is integrated in phonelines..
In cable connections, if many of you are subscriber in your locality most likely you will experience heavy internet traffic during Christmas and holidays...unlike DSL or broadband..
Go for DSL....I think AT&T is the best... Many claim to be fast but, I will choose a established company and also they are cheaper than other.