My all time favorite song to play is Ozzy Osbourne's Mr. Crowley (Live version). The way I play it is a combination of live recordings of Randy's way, Jake E. Lee's, A Zakk Wyldes. The rythum is probably one of his his easiest the songs to learn but I never tire of playing it. Adding different nuances of the above mentioned players I believe has made me a better player in both phrasing and feeling.
But of course I enjoy anything Ozzy has done from The Sabbath years, solo years, and the Miss Piggy years.
I started learning guitar because of Randy Rhoads..but Yngwie J. Malmsteen is my biggest influence.