I Wanna Be the Boshy/YMMV

Best Boss Ever: Many, though Ryu and Missingno are common choices.
Breather Boss: None of the bosses are really easy, but there are plenty, mostly surrounding the main trio.
Most Annoying Sound: "It's Boshy Time!"- You will hear it every time you hit retry.
- Ryu and Sagat have "Final round: FIGHT!" every time, which may well be even more annoying.
That One Boss: Mario, Sonic, and Mega Man are far and wide considered the most difficult of the eleven main bosses. The final boss is in a category all its own.
That One Room: The Spike Room. You will die thousands of times before getting past it.