Music. Music is an auditory experience, first and foremost, and "editing" would be the process by which I tried to attach visuals to that experience. Music creates emotions and ideas which are totally unique in my head, and that is what I enjoy most about making AMVs: taking what's in my head and trying to duplicate and share that with others. Consequently, it's extremely easy for me to hear a song that conjures really strong ideas and in the next nanosecond be thinking "How can I make an AMV out of this? What anime can I use?" I guess you also could argue that, in most cases, the music in AMVs remains the most true to the source material. The anime we bend and twist to all sorts of purposes and shovel on all kinds of effects, but the music is usually left in its original state.
I haven't ever really watched an anime series and then thought "How can I make an AMV out of this? What song can I use?" Anime doesn't inspire the same kneejerk reaction to think about editing, perhaps because it's too visual. It's hard for me to take someone else's "editing" and ideas, process it and come up with a new idea that will create new visuals or attempt to capture the essence of the original. Kind of feels like when I need to do math, my brain just kind of goes "derp." Wipe the slate clean with music, though, switch to the other side of my brain, and I have no problems whatsoever.