Dio for sure.
Dio had this particular amazing voice range and he was such a nice man, but Ozzy is more fun. I vote Ozzy.
For Black Sabbath, I prefer Ozzy. But Dio did some great work with Sabbath, and I really liked his solo work and with Rainbow. "The Last in Line," "Rainbow in the Dark" and "Holy Diver" are some of my favorite songs.
By far in Black Sabbath Ozzy was the best. Ozzy is great and I love him but I have to say that DIO did a lot for the music and the world
DIO. No doubt about it.........