1989, then, in order, 1996, 1979, 1993, 1977, etc. No question that 1996 is riveting and amazing, but 1989 has always been in my mind the standard of a perfect hornline. Not just technique, but for feeling and emotion, they were walking on water. Not that '96 didn't have its emotional moments, but I've always seen that show as a bleak portrait...a lot of it had to be painted in a very stoic manner--so a lot of the emotion came from audience response.
'89 by a slim margin, IMHO.