Hi
AMG, the professional database, freedb the free database and others are inconsistent. iTunes seems to take most of the info from AMG.
However sometimes iTunen is the best sometimes not.
For ripping I do the following:
1) I Try JRiver, if its complete regarding tags or sufficient I go with it (rip)
2) if not I go to dBpowerrmap if okay i go with it (rip): its the best for classical music, however not at all complete nor correct all the times
3) iTunes, has sometimes only tags. I rip with iTunes (ALAC lossless similar to flac, secure rip inside iTunes) it embeds all tags from iTunes as well as cover art. Then load it in JRiver, convert to flac. Then edit tags.
My library has only flac and mp3, nothing else. I convert all other formats to either flac (if the other format is lossless) or mp3 if the other format is lossy.
Peter