I agree with the first 2, because they don't add anything descriptive, they deny the humanity of the person and indicate that a person is lesser. Mentally retarded means exactly what it means. Handicapable means nothing, and special needs means nothing at all. It's not political correctness not to say the n word, it's a desire not to insult. Mentally retarded or shorthand retard means what it means, and I'm not in favor of saying we have to say words that mean nothing so as not to offend people.
I also call dumb people retards.