Personally I never did Genocide. Flowey's parting words really hit home.
I did however use a save editor to make a separate file so I could skip to the Undyne and Sans fights, because Sans was right when he said I was a bit of a freak. I Quit before dealing the final blows though!!
Theres no point quitting before finishing off Undyne the Undying. Contrary to her name, she is very much dying as I recall, only holding on through determination. Also her death on a neutral route is a lot sadder, you should go see it if you havent ---
Rally for Kirby in Character Battle X! He is the true hero of Nintendo!