My favorites are Motorbreath, Escape, and Til It Sleeps, although that's a great song too.Fade to Black is their best song.
Cliff was such an amazing bassist, he was really into like hardcore punk like The Misfits and Black Sabbath, and I think he influenced a lot of their early sound. He had a real melodic way of playing that kinda transcended the typical confines of the instrument.Also, Cliff Burton's Bass Solo: Pulling Teeth. Who else ever had a bass solo?
He did such an amazing job no one dared.