I think the worst CD I have listened to, for both sound quality and content, is Metallica's St Anger. Really harsh sounding, especially on the drum symbols.

For one of the best rock CD recordings, I would have to go with the MFSL Gold Version of Guns N Roses' Apettite for Destruction. The beginning of "Mr Brownstone" is just amazing - really tight bass. For DVD-A/SACD, you really can't go wrong with The Who's "Tommy" on either hi-res format.