Vergillicious
You will not forget this devil's power!
And yes, you can only pick one. No "I can't there's so many to chose from" just pick one from what's the best and worst in your opinion.
I searched high&low and i think i've found at least one of the worst anime ever made which is fairly popular :-And I'm not gonna choose the worst anime because I believe that every anime, however bad it may be, got some positive things in it.