Broadway Legend Joined: 2/10/11
Can be supporting or lead.  My choices.
 
Actor -- Musical:
Nathan Lane -- The Producers
Phil Silvers -- A Funny Thing Happened
Lenny Baker -- I Love My Wife
 
Actress -- Musical:
Barbara Harris -- The Apple Tree
Beatrice Arthur -- Mame
Beatrice Lillie -- Hugh Spirits
 
Actor -- Play:
James Corden -- One man, Two Governor
Philip Bosco -- Lend Me a Tenor
George Rose -- My Fat Friend
 
Actress -- Play:
Maggie Smith -- Lettice and Lovage
Maggie Smith -- Private Lives
Angela Lansbury -- Blithe Spirit
 
Some of the top of my head would be:
Nathan Lane and Gary Beach in The Producers
Mark Rylance in Twelfth Night
Daveed Diggs in Hamilton
Jeff McCarthy in Urinetown (granted, everyone was hilarious in that cast, but he really stood out)
Really the whole cast of the recent Noises Off since it’s such a team effort, but the real standouts were Megan Hilty, David Furr, and Andrea Martin
Bertie Carvel in Matilda (Gabriel Ebert and Lesli Margherita were also hysterical)
James Corden in One Man, Two Guvnors
Andrew Rannells and Josh Gad in Book of Mormon
Christian Borle in Peter and the Starcatcher and Something Rotten
Sure there’s other examples that’ll come to me later
Bernadette Peters in Hello, Dolly.
Broadway Legend Joined: 4/14/11
Not sure I'd say this is the greatest I've ever seen, but I feel Josh Gad in Mormon was by far one of the most underappreciated performances of the past decade. I don't know that I've ever seen another performer strike as perfect of a mix between being big and goofy and funny and over-the-top with just the exact right amount of warmth and heart and realness underneath it all which he never lost sight of throughout the show and really made you love and cheer so hard for his character as a result.
CHRISTOPHER FITZGERALD in Waitress 1000000%. The definition of a scene-stealing performance. One of the best performances I've ever seen, period.
The first ones that came to my mind were the following:
Nathan Lane - The Producers
Christine Baranski - Rumors
Sara Ramirez - Spamalot
Stand-by Joined: 3/2/15
Dorothy Loudon in "Annie."  Judy Holliday in "Bells Are Ringing."
And another vote for Maggie Smith in "Private Lives."
		     			I’ll jump on the bandwagon and say that I was lucky enough to see Nathan Lane from the center orchestra during previews for The Producers and it remains the greatest musical comedy performance I’ve ever seen. Of course, he had good material! 
 
In terms of turning straw into gold however, Mark Rylance was pure genius in Boeing-Boeing. 
 
		     				
		     					
Featured Actor Joined: 1/4/11
Norbert Leo Butz - Dirty Rotten Scoundrels
Steven Boyer - Hands to God
Stand-by Joined: 7/27/11
Geraldine McEwan and Richard Briers in the 1998 Broadway production of The Chairs.
 
(and, of course, Nathan Lane in The Producers)
I will just list the first one that came to mind. I know not many had the chance to catch it at Encores but Christine Baranski in Promises, Promises. In her very limited time onstage she stole the show. 
Not the best quality but there is a clip online.
https://www.youtube.com/watch?v=m0TYj1Hvc9U
These performances come immediately to mind:
George Hearn, La Cage aux Folles
Michael Jeter, Grand Hotel
James Corden and Tom Edden, One Man, Two Guvnors
Christian Borle, Peter and the Starcatcher
 
Faith Prince, Guys and Dolls
Mercedes Ruehl, Lost in Yonkers
Jan Maxwell, The Royal Family
Mark Rylance, Boeing-Boeing and La Bête
Christopher Plummer, Barrymore
Julie White, The Little Dog Luaghed
The two actors performing in Sleuth at a theater in Dublin, Ireland in the early-mid 90s. I can't remember their names or the name of the theater.
 
 
 
 
Broadway Legend Joined: 2/10/11
cliffordbradshaw2 said: "Dorothy Loudon in "Annie." Judy Holliday in "Bells Are Ringing."
And another vote for Maggie Smith in "Private Lives.""
You saw Judy Holliday in Bells Are Ringing?  If I could go back in time and see 3 or 4 performances that I was unable to see, Judy Holliday in Bells Are Ringing would be one of them.  I still play the OCR regularly, although it is relatively short.  I have cut the Midas Touch, I seem to recall a Beatnik number, and at least one other song.  What's left represents an incredible score AND audible proof that her live performance must have been incredible.
The funniest performance I ever saw in a show was Christian Borle in Peter and the Starcatchers. There's a moment - if you've seen the show you know what I mean - that stopped the show dead for a solid three or four minutes because the laughter was so extreme. I've never laughed that hard in a theater, and I saw Nathan Lane in The Producers (my runner up choice).
Andy Karl’s physical comedy in Groundhog Day was only amplified by the huge heart and depth he played Phil with. Really wish he had gotten the recognition he deserved for that role.
VotePeron said: "Andy Karl’s physical comedy in Groundhog Day was only amplified by the huge heart and depth he played Phil with. Really wish he had gotten the recognition he deserved for that role. "
To be fair, given his precursor run, he probably would’ve won if it weren’t for him being up against such an undeniable performance in a way bigger show.
Mulaney and Kroll in Oh Hello! Obviously not a traditional play with traditional actors, but definitely the funniest thing I've seen on a Broadway stage. 
 
Pretty recent, but I really though Sarah Stiles in Tootsie was just stellar. I really enjoyed most of the cast in that show anyways but Sarah was absolutely incredible in that role.
Leading Actor Joined: 12/10/18
James Corden - One Man Two Guvnors
Mark Rylance - Twelfth Night
Rick Holmes - Peter & The Starcatcher at New World Stages as Black Stache. Absolutely stole the show, pure brilliance. I also saw Borle, but he had nothing on what Holmes managed to do. Went back to see the closing performance just for him.
John Cameron Mitchell - Hedwig (Broadway, CRATE)
Broadway Legend Joined: 7/22/03
Lily Tomlin - The Search for Signs of Intelligent Life in The Universe
 
 
I'm going to throw in a vote for Peter Gallagher for the revival of On the Twentieth Century. I didn't think he was giving anything away to John Cullum, but he wasn't even nominated. He slid under the radar, as did the show pretty much after it flopped in the Tonys.
 
And I'll see you a Christine, and raise you a Katie. They were both great in a great role. Katie won the Tony.
I forgot how to make the video stop, so this goes on for another minute after Katie.
https://youtu.be/ACctFwjkAzI?t=510
 
 
The original Broadway cast of Gods of Carnage. That foursome had perhaps the greatest timing and chemistry I’ve ever seen on stage. I’ve never laughed so hard in the legitimate theater in my life as I did that night.
The first one that comes to mind is Mark Rylance in Boeing-Boeing.
Actor -- Musical:
Bertie Carvel - Matilda
Matt Doyle - Company
Josh Gad - The Book of Mormon
Andy Karl - Groundhog Day and On the Twentieth Century
Andrew Rannells - The Book of Mormon
Ethan Slater - SpongeBob SquarePants
Taylor Trensch - Hello, Dolly!
 
Actress -- Musical:
Laura Benanti - She Loves Me
Bette Midler - Hello, Dolly!
Kate Rockwell - Mean Girls
Jennifer Simard - Company, Disaster, and Hello, Dolly!
Sarah Stiles - Tootsie
Alyssa Umphress - On the Town
Helene Yorke - Bullets Over Broadway
 
Actor -- Play:
Steven Boyer - Hand to God
Sean Hayes - An Act of God
Marc Kudisch - Hand to God
Michael Oberholtzer - Hand to God
Actress -- Play:
Laura Benanti - Meteor Shower
Megan Hilty - Noises Off
Geneva Karr - Hand to God
Sarah Stiles - Hand to God
Stand-by Joined: 7/5/11
Laura Benanti in Women on the Verge of a Nervous Breakdown remains one of my all time favorite comedic performances.
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