Kor has my vote. Several things; he was the first and that always makes a difference. Also, he had a quieter approach, as someone (or more) indicated, he smiled while being ready to kill - could really throw you off-guard. I think the quieter ones are usually the ones that you have to watch out for. Kang was very good, and yes Michael Ansara had a great look, but I'll go with John Colicos's Kor. As much as I liked William Campbell (loved Trelane), he didn't make a good Klingon. I don't know if it was the way it was written, or directed, or if it was his interpretation - whatever, it didn't work.