If you are primarily interested in Netflix, you may want to see if you can find an ISP who is part of their OpenConnect program. Only members of Netflix's OpenConnect program will be able to stream in Super HD quality or above.
Unfortunately, Time Warner is NOT a member - they refused to join earlier this year when asked, even though it is free. I am not sure about Comcast, but they aren't explicitly listed, either (though I heard they are getting on board, I can't confirm).
From Netflix's site:
ISPs can directly connect their networks to Open Connect for free. ISPs can do this either by free peering with us at common Internet exchanges, or can save even more transit costs by putting our free storage appliances in or near their network.
Major ISPs around the world have already connected to Open Connect, including Frontier, British Telecom, TDC, Clearwire, GVT, Telus, Bell Canada, Virgin, Cablevision, Google Fiber, Telmex, and more.
For more information, visit:
https://signup.netflix.com/openconnect
This link can check if your current ISP allows for SuperHD :
https://signup.netflix.com/superhd
Comcast does rate pretty highly in terms of average streem speed for netflix, even if they are not in the super HD program:
http://blog.netflix.com/2012/12/november-isp-rankings-for-usa.html