Hmmmm . . . once I bought real expensive tickets for Tom Petty and company because I wanted to see Lucinda Williams and her band who was opening for him.
I thought Patty Griffin was a good opener for Lucinda and her band back in The Car Wheels days.
Back in (I think) 1980 we went to see South Side Johnny And The Asbury Jukes at The Kiel Opera House and I thought that John Mellencamp (who was John Cougar at the time) put on a better show.
Going back even further, Sammy Hagar opening for Boston and on another occasion Thin Lizzy opening for Nazareth.
I saw Jill Sobule open for Warren Zevon a couple of times and I always thought she was pretty good.