Discogs

There is no rival.

Recently, Discogs have taken off buy links for most bootleg and pirate releases, possibly under pressure from artists, labels, RIAA, IFPI, PRS and other organisations.  Some still remain as it'd take forever to get them all.  I know I bought some pirates from there when I had the chance (I can't remember buying bootlegs online except in trade from Ukraine).  Seldom do they find their way in brick and mortars in the west that I've seen lately.  I still get them my usual way when I can.
I use Discogs to keep track of my entire collection and it has gone to over 2,000 items, enough to open a shop!  I can't add or edit releases there anymore, but I check to see if there's a match once in a while for something I have that they didn't.