The best concert for me was probably the Barenaked Ladies on their Maroon tour. I was in high school, they were my favorite band, and the night was just amazing. They always talk on stage and do a little improv and you don't go "Oh my God, I just saw the Barenaked Ladies!" you go "Oh my God, that was a lot of fun!" and it's really refreshing.
It's a toss-up for worst concert though. Everclear was BAD. It was even the first night of the tour and they just had no energy at all. The other one was back when Nintendo did the Fusion tour and Hawthorne Heights was the headliner. A bunch of friends went with me because the lobby of the venue was going to have the Wii set up and playable, long before it launched. The demo units kept crashing and the only game any of them got to actually play was Excitetruck. I was actually there for the concert, but it was in a big high school auditorium and they had the speaker set-up for a stadium. Couldn't hear for days afterward. Hawthorne Heights and Reliant K were terrible live. The only highlight of the evening was the very first opening band. It was the Plain White T's and they started the night with "We're going to do a song we've just finished and never performed live: Hey There Delilah" and then it was fun to see how big that song got about a year after that when they hit it big.
