Best:

The Darkness at Wembley, December 2004.
I know they're epically gay and incredibly cheesy, but they put on a hell of a show.
The sound was incredible quality, they're brilliant players.
Justin interacted with the crowd in a great way, everyone was laughing and cheering from start to finish.
And of course, how can you speak ill of someone who plays a solo while sat on a giant arctic tiger, suspended no more than 6 feet above the crowd!

As for the worst I've only been to a few gigs, and none have been "bad" as per say.