These albums are truly quite hard to pair up in a head-to-head match, mostly because they are so dissimilar. I'm familiar with both records, but for this game I listened to each song pair at a time and in the end, Black Sabbath is my hands down winner.
Paranoid and Machine Head are both incredible albums, but one is a brilliant early heavy metal album and the other is a great hard blues rock album. The uniqueness in what Sabbath is doing, from the music, to the mood, to the lyrics, is simply at a higher level than the expertly-played blues that Purple pumps out here. Don't get me wrong, I love these Purple songs, but the Sabbath tunes are iconic and varied. Every time I played these songs in pairs I thought, "WTF is Sabbath doing, this is exciting!" and then thought, "Yeah, Purple's playing some fun blues." It even shows in the lyrics. Ozzy's belting about war, giant robot monsters, evil, faeries, and a bunch of other drug trip shit, and Ian Gillan's talking about cars, trucks, and literally being lazy and sleeping - one is just so much more inspired and inspiring.
Smoke on the Water gets my sole vote for Purple because the riff, lyrics, and overall feel of the song far surpass Electric Funeral (which is probably the weakest overall song on Paranoid and also the most jumbled together). The thing is, even when these Sabbath songs seem shaky in structure or a little meandering, they're still more engaging than stuff like Lazy (which is literally just a giant blues jam).