Hard Question Nando.
Probably 'Sabbath Bloody Sabbath' as a complete worx... with 'Vol 4' a close runner up. But listening over the past two days, if you would have asked me early on, I would have said 'Vol 4' straight away. Then there's the whole post-Ozzy period. And the reunion run. Lots of good stuff over the decades - but the original Ozzy catalog is my favorite encyclopedia of Sabbath
I like 'The Last Supper' live album very much. Excellent capture of their mastery, with lock step percussion & bass.
The concert video is cool too, but they interrupt some good jam runs with backstage and interview, tom foolery.