All I read is how bad cable (SDTV) is on an HDTV.
Welcome, Larry.
The reality is that this is all over the map. Frankly, the basic analog channels aren't bad here on Insight, now Comcast in Rockford.
However, the system does offer a digital package upgrade. What surprised me was that virtually all the analog channels were duplicated in digital on the basic digital tier. That makes for a pretty solid picture. I would definitely look into upgrading to this.
Comcast is offering a digital package, as are both sat providers. They tend to be fairly comparable over the long run, but there are short term differences where one gets ahead of the others for awhile. It kind of boils down to three factors in deciding between them. First, many carriers compress their signal and reduce bandwith/resolution. Currently, I would say the picture quality in descending order is OTA, DTV, Cable, DISH. This is likelyto be a controversial statement and others will express different opinions. YMMV.
Second factor is usability of the box. I would definitely recommend some form of DVR. Once you have one, you never look back and can't live without it. My personal preferences here are DISH, DTV, COMCAST in descending order of usability.
Third factor is HD programming choices. They mostly all have the same choices for SD, at similar prices. Right now DTV is the clear leader. I would say overall DISH is in second and COMCAST third, but this varies widely. COMCAST is promising a lot in the next few months here. DISH says "soon", and it is dependent on 2 satellite launches this spring.
Yes, you will notice a difference between HD and SD on your set. However, very little is currently available in HD yet and even the HD stations do a lot of upconverting. IMHO, nobody ever does upconverting right, and you are often better off looking at the SD feed.
OK, that's probably more than enough for now. Good luck on your quest.