i am no expert when it comes to sierra music, only recently have i started listening to it seriously. however as it stands, i beleive that gabriel knight 3 and QFGV have the best scores. as a filmmaker i appreciate the cinematic feel these two have. they set the moods perfectly and to this day, when i hear that theme from gabriel knight it gives me chills.
infact this is why i encorperated the gk3 score into my latest film. holmes and henry did a superb job.
This isn't a fair assessment of Sierra soundtracks, since your two favorites are digital scores performed with real orchestras. You can't really compare that to a MIDI soundtrack, as was used in most Sierra games.
But even so, that doesn't say anything about the quality of the compositions; only the overall sound quality of the score. I believe between Chris Brayman and Mark Seibert, Sierra has produced much better music than just what's heard in these two games. In fact, I feel Robert Holmes did a better job with his first Gabriel Knight score...in terms of writing.