Hmm... brain damage or the possibility of getting hit in the theigh because nobody is that precise with their strikes. The roundhouse kick is nice and balanced. Side kick is cool. But you're still wrong. If your opponent is rushing you and you're trying to throw a side-kick your American Krotty is going to get yourself pounded. Meet his force with your own force or if you're fast and reactive enough move the **** out of the way and kick him.
Wait, what? Are you saying that If I was being attacked, a kick to the head would damage my rushing opponent more than a kick to the knee or groin? Imagine yourself in the position of the attacker. Would you rather get kicked with a round kick to the head, or a side kick to the knee? The round kick has a chance to stun. The side kick has a larger chance to stun, stop, and disable.
Best Clean kick: Karate Side Kick. Hands down.