Top ten, this feels impossible (no particular order, not necessarily considered icons):
Patti LuPone, Audra McDonald, Chita Rivera, Kelli O’Hara, Lea Salonga, Alan Cumming, Mandy Patinkin, Cynthia Erivo, Judith Light, Sutton Foster.
Beyond the parameters of ten (always honored to see them on stage, not all icons, but I would highly recommend):
Patti LuPone, Chita Rivera, Audra McDonald, Kelli O’Hara, Mandy Patinkin, Lea Salonga, Alan Cumming, Judith Light, Laurie Metcalf, Sutton Foster, Laura Benanti, Glenn Close, Judy Kuhn, Mary-Louise Parker, Raul Esparza, Tyne Daly, Bernadette Peters, Bebe Neuwirth, Megan Hilty Neil Patrick Harris, Joel Grey, Brian Stokes Mitchell, Andre deSheilds, Joshua Henry, Jonathan Groff, Jane Houdyshell, Mark Rylance, Kevin Klein, Cynthia Erivo, Stephanie J. Block, Lindsay Mendez, Shoshana Bean, Jessie Mueller, Annaleigh Ashford, Lauren Patten, Stephen Pasquale, Phillipa Soo, Renee Elise Goldsberry, Patina Miller, Leslie Odom Jr., Christopher Jackson, Adrienne Warren, Jennifer Simard, Sherie Renee Scott, Heather Headley, Ruthie Ann Miles, Celia Keenan Bolger, Gavin Creel, Priscilla Lopez, Liza Minnelli, Beth Malone, Liz Callaway, Danny Burstein, Rob McClure, Mykal Kilgore, Bonnie Milligan, Ashley Parks, Josh Gad, Andrew Rannels, Ben Platt, Patti Murin, Cassie Levy, Jessica Vosk, Alex Newell, Jenn Colella, Grace McLean, Ruben Santiago Hudson, Brooks Ashmanskas, Beth Leavel, Brandon Victor Dixon, Rachel Bay Jones, Christian Borle, The Bengsons, Carmen Cusack, Tony Yazbeck, Mary Testa, and and and…