Ah, this thread. Okay, lets see if my favorite has been posted... hmm, OP posted it. Maybe second (Flash)? Nope, already page 1. Maybe Supermans speech to Darkseid? Nope.
Well, then the one Avatar fight that hasn't been posted yet which was disturbing and tense at the same time:
The perspective, the timing, the few spoken lines, the colours used, the animation quality of the moves themselfes... No, no scene from any anime / cartoon can top this. They have yet to display the amount of unrealism in such a realistic way.
This little fight shows the development Zuko went through, the mental state of Azula and how she thought of everyone else in terms of power.
"I'm sorry it has to end this way, brother!" "No, you're not."