I would have said "Amok Time" with Celia Lovsky, Arlene Martel and Lawrence Montaigne was the best. Runners up include "Bread and Circuses" (William Smithers, Logan Ramsey, Ian Wolfe, Rhodes Reason and Lois Jewell), WNMHGB and a guilty pleasure, "Wink Of An Eye" with Kathie Browne and Jason Evers. Of course the all time greatest guest star was William Windom, hands down!
I left out Amok Time on purpose---Montaigne has exactly two lines--I'm sorry that's not a signiicant supporting role IMO. He just had to stand there and look annoyed. If he hadn't played the bigger part in Balence--nobody would have much noted him in this episode.
As for Bread and Circuses--yes Wolfe, Reason, Smithers and Ramsey are perfect for a 2nd poll but Lois Jewell?
MOST episodes include at least 4 guest actors--I am purposely NOT including certain episodes because then you could under that theory include Doomsday Machine by listing 1 to 2 line extras such as Burns, Compton, Catron, Copage along with Windom as an "ensemble' cast---
which then means people who love Windom's performance could choose that episode just as if they were voting in 'best guest actor' poll.
I really want to spotlight episodes where they had a fairly large guest cast with solid medium to large parts.
That's why I included Archons even though I figured it would struggle to get any votes.
You had 4 to 5 solid chatacter actors in one episode which is kind of nice to see.
Wouldn't it have been nice for Montalban to have at least one follower have a decent part besides that lame Jaquin actor who barely has 5 roles in his career?