Excluding anime, because that feels like cheating to have music made by professionals in the music industry involved:

Best Intro Song Hands Down: Class of 3000 tied with Code Lyoko ( either French or English because they’re both amazing )

Worst Intro Song: Regular Show ( it’s just a sound effect AFAIK and barely constitutes an intro song in my opinion )

As for sequence, that’s a tougher question for me.

Best Intro Sequence: A tie between BTAS, Batman Beyond/of the Future in Europe, I guess, and Code Lyoko seasons 2-4

Worst Intro Sequence: Regular Show ( it feels like a powerpoint presentation with an ongoing sound effect in the background to me )