Among my favorites would be the Countess Aurelia, Julian and Nina in Dear World; Dolly, Cornelius, Irene, Barnaby and Minnie in Hello, Dolly!, Diana in The Happiest Girl in the World, Barnaby and Nancy in Sail Away; Audrey in Let It Ride!; Laura in Tenderloin; Eileen in Wonderful Town...
I try not to think about the ones I couldn't stand. Wasn't being in their presence in the theatre painful enough? But since the question has been posed, I'll shudder and answer: Sweeney Todd, Fosca, Ben Stone, Buddy, George, Charley Kringas, Bobby Baby, Che, and I'm sure many more I've forgotten ----- forever, I hope!