I've been using MyHD cards for OTA HD for about a year and a half now, I've also got a Dish 811, and have also seen a fair bit of FTA HD from C and KU band. I've also got a 4dtv receiver that I've watched SD on, and will soon have HD capability via an r5000hd mod.
From all the sources I've seen, HD is definitely better than 4dtv SD content. Some of my OTA channels are quite awesome. I watch them on a 100" screen projected with an Infocus X1 projector, and also on a 32" Sony LCD. Football is the best as its shot with HD cameras. The film transfers done with most TV shows and movies vary in quality. I think it has a lot to do with the quality of the equipment used to shoot the program. They're still generally a lot better than SD. The C and KU HD can also be extraordinary. Again the source material tends to be the deciding factor, but sports are awesome and TV shows and movies vary but are always way better than SD. Dish network HD is usually better than 4dtv SD, although the Voom channels are just mediocre in my opinion. I'm not sure if that's do to HD-Lite or just poor source material. Dish also tends to have some artifacts in their picture which I would assume are the result of too much compression.
After all that is said, the first generation 4dtv/Cband SD signal is without a doubt the best SD I've ever seen. They totally blow away the pizza dishes. Some of the channels that NPS reuplinks, are of similar quality to Dish however.