Ok.. Wow that's a hard one.. Pick just one??? Not sure I can...... But here's some of My favorits..
Operation Rock and Roll, Summer of 1991, Judas Priest, Alice Cooper, Motorhead, Metal Church and Dangerous Toys
Metallica w/ Queensryche Spring 1989
Metallica w/ The Cult Summer 1989
Overkill w/ Dark Angel and a couple local bands.. L'amour 1990
Sepultura with a few local bands L'amour 1989
Lizzy Borden with a couple local bands L'amour 1989 I think??
Crimson Glory at some club called Zone dk in NYC 1990 I think?? coulda been 1991...
Kiss w/ Skid Row and Ted Nugent October 2000
Queensryche w/ Type O Negative Summer of 1994...
And that's just off the top of My head.. Hard to pick just one....