I don't really care about deep purple. I like the organ solo on Highway Star and Smoke on the water has a good riff, just a shame about the rest of the song. Beyond that I don't know their work. Sabbath essentially invented Heavy Metal just with the first three chords on their first album. I know there's great monsterfuzz and other proto-metal, but nothing from before that track sounds as complete, as fully-formed in its metalness as that opener. So they get mad props for that. Led Zep just have it musically, I think. What Bonham was doing on that drumkit just wasn't happening elsewhere in rock music. He was bringing in this jazz, funk and soul stuff and giving everything so much texture, throwing in triplets and following the guitar through the solos instead of locking in with the bass. Same can be said of JPJ, Page and Plant get all the glory but that rythmn section were the true innovators. But I saw Sabbath live and they kicked it, so I'll go with them
That is a difficult question to answer. Mostly because people's opinions are going to vary vastly. While I do have several Zeppelin records I would have to give the edge to Sabbath. There certainly isn't anything wrong with Deep Purple. Regarding Deep Purple I have been enjoying the song "Space Truckin'". (Smoke...Water, Highway Star, etc are all good songs in their own right).