Let's see...
#1 - A tie. I sat 5th row floor, seats 1&2 for Billy Joel and Elton John Face 2 Face this year in Indianapolis, IN, and sat 2nd row floor seats 1 & 2 for Weird Al Yankovic last year on July 3rd in Louisville, KY. I listen to a LOT of music, but those are my 2 favorite concerts. I've seen Al 5 times now, Billy and Elton 3 times, and just Billy once.
#2 - Worst absolutely had to be 'N Sync' - I had to go to this show with the wife to get her to go to our first Billy & Elton concert - after the first show, though, she will go and see Billy and Elton anytime!
#3 - Show I wish I'd gone to? The Billy Joel Y2K concert on 12/31/99 in NYC. I'm an IT guy, and no matter how hard I tried, there was no getting off work on 12/31/99 because of Y2K. So, I spent that new years eve at work watching nothing happen :)
