I would probably vote for Sabotage on the strength of Symptom of the Universe alone, but the whole album is consistently strong and heavy. Ironically, while the band were at a creative peak, they were experiencing management and record company problems, so this was the last great Osbourne-era album. I remember hearing it as an import, before it was released in the UK, which was a sure sign something was wrong.
Volume 4 has Snowblind and Wheels of Confusion, which stand alongside anything by the band, while Laguna Sunrise and Supernaut are okay, but that is it for me. Sabbath were full of coke and the album title shows the lack of inspiration. I do like the front cover, which was designed in about 10 seconds, but it works. You could always spot it in the record shops.