I haven't listened to them all in entirety so it's hard to say fairly. Blizzard was one of the first albums I ever listened to and I have some really nice memories attached to it. I think Blizzard sticks with me as having more sentimental appeal, whereas Diary comes close in that respect but maybe comes out a bit above Blizzard in terms of being musically interesting. Bark at the Moon and Ultimate Sin have some of my favorite Ozzy songs and I like the stylistic progression even if they 80s'd it up. I just can't put them above the first two, given my sentiment.
I can't make a good quality judgement because I'm so wrapped up in the nostalgia I have attached to his first two; I even love Black Rain a lot (and I got sentiment for that one too) , and for all I know that could be a better album by my standards, and I'd still be talking about Blizzard and Diary.
I'll go with Diary tbh, but not by much.