I like the palm heal strike for self defense, but only to the face/chin/neck. I wouldn't want to risk breaking my hand while trying to strike the head with a closed fist. Even though the neck is a soft surface, I'd still use my palm heal to strike the neck. It has become a conditioned response for self defense strikes to the face/chin so I think it would be easiest to just use the same strike at the neck.
The self defense seminars I've been too have advocated the palm heal as opposed to a closed fist for women in self defense situations. Maybe because a lot of women don't make a fist the "right" way and are, therefore, more likely to break their hands/wrists on an attackers face.