Oz man for me, Dio has a lot more history to his work, but Ozzy excites me more.
Dio is an artist whose full catalog I am still making my way through, Ozzy's I am very familiar with, but from a Sabbath point of view, I have got to agree that Sabbath with Dio was essentially Rainbow 2.0. Are they good records? Yes. Are they Sabbath records? Debatable, but I'd go with no.
Just my two cents.
Yesterday don't mean SHIT.