Here's an all around poll for the favorite stage in Mega Man 2. You can base your criteria on anything you want, whether it be music, level design, or the boss fight.
Just pick your overall favorite stage to play. I'm curious. I'm probably going to do this for the NES Mega Man games. I decided to skip Mega Man 1 because:
A) Few people have played it
B) Nobody cares about it
So Mega Man 2 is up. Feel free to comment on your favorite stage too.