What’s up with these “if you could only pick one” threads? Single special edition change you’d keep? Single special edition change you’d remove? It’s as though you’re about to be dismembered and the executioner asks you “which limb would you like to keep?”. Impossible it is to choose a single problem to take away from the prequels and SEs, because it’s the sum of everything that makes them crap.
As for the topic in question, does it pertain to backstory that was ruined or anything you can think of? In the latter case, one could simply “win” by picking the story of some background character. I bet nobody would flip out if they discovered Dr. Evazan was IG88’s lover.
If it’s the former, however, I suppose I’d pick Palpatine since it was the charcter whose dignity was hurt the least.