Favourite scene / favourite fight?
For me I absolutely love the Amp vs Amp, Sex Bob-Omb vs Katayanagi Twins fight.
I liked it because it was different from the other battles in which the characters physically fought against each other, instead this was a battle of music...or at least loudness! Having the fight played out between conceptual mythical creatures was a brilliant touch as well. I also liked the twins turning their amps up to 11 as well!
The main reason though was that it was the band's best performance throughout the film: The song they played was really good and rocking, and you could see that all the band members were giving it everything, which they hadn't really done until that point (apart from maybe the opening credits).