Krayt, Caedus and Kun were mediocry intelligent people, which sets them as some ****ing god-tier of the Star Wars universe, ROFL.
Shimrra has the excuse of being mind-controlled, so there's that, while Nyax at least suffered a legitimate, physical brain damage.
All the others are so retarded it's hard to chose who's more disabled, except Abeloth, who takes place 1.