I'm months late to the original post, but wanted to chime in.
Man...good topic, and tough to do. But as complete albums, I'm split. I'd take Holy Diver over Blizzard of Ozz. I just think it's slightly ahead of it in terms of songwriting and performance. But it's SO close. Last in Line vs. Diary of a Madman....again, SO close. But I am clearer that Diary is better.
BUT, because I am much more clear that Diary is better than Last in Line, I think that swings me to Ozzy by an absolute hair. I favor Dio as a singer by a mile. But comparing just these first two solo albums, I have to give that thinnest of edge to Ozzy.
Great OP.