My observations, with a new plasma TV (with built-in freeview decoder), are that most digital channels are compressed to the point that it is impossible to obtain a decent image without pixelation, particularly with movement.
I noticed this also with our old CRT TV and cable TV.
The 5 analog channels via our roof aerial are better than the equivalent via cable, and about equal to the digital freeview received via the same roof aerial. The signal strength is excellent, so that isn't a problem.
Apart from BBC1 & 2, ITV1 and C4, all the remaining freeview channels are of poor quality, some no better than i-player. There is an enormous difference in picture quality between ITV1 and ITV4, for example, or between BBC1 and "red-button" BBC channels (noticed particularly during Wimbledon).
I would prefer that the spectrum available after the analog channels are switched off be used to increase the bandwidth for existing freeview digital channels rather than used to provide lots of HD channels, although it would be great to have a few freeview HD channels! Save me putting up a satellite dish!
SD