This is like asking a parent "who is your favorite child?" Far too many to choose from. Here's my fave song from each album:

BLIZZARD OF OZ: Crazy Train
DIARY OF A MADMAN: Diary of a Madman
BARK AT THE MOON: Bark at the Moon
THE ULTIMATE SIN: Killer of Giants
NO REST FOR THE WICKED: Bloodbath in Paradise
NO MORE TEARS: I Don't Want To Change the World
OZZMOSIS: See You On The Other Side
DOWN TO EARTH: Gets Me Through
BLACK RAIN: I Don't Wanna Stop

I guess the answer lies somewhere in there. :o)