what.cd and waffles have the most FLAC torrents. Youll find almost everything there.
Pedros, iTS and Exigo is aimed towards high quality which includes high quality scans of covers booklets along with proper ripped FLAC's.
Yes Pedros has a decent collection of Jazz and Classical music. For jazz i think the best tracker would be vibes.fm That tracker is focused on jazz only.

Hope this helps