'Hole in the Sky' is my all time favorite Sabbath song. That guitar & bass riff is so evil. Ozzys vocals and lyrics are icing on the cake. The only time I didn't like that song is when Metallica covered it at the HOF tribute. Every Sabbath recording I've ever heard live is amazing...as was Pantera's cover. If Ozzy can't hit the high notes on this tune, let him sing it low like Phil did...it sounded great that way.

Second choice would be 'Diary'...which I know has rarely ever been covered live. I think Gus G has exactly the right chops to pull off this song live.