I’d have to go with what is probably the more obvious choice, Waiting Godot. It was the first Beckett play I read and it left me amazed. I found Endgame equally as fascinating, just minus the novelty factor, since stylistically and thematically it’s quite similar to Godot. Have you read any of his novels? So far I’ve only read Molly and Malone Dies. They’re quite funny but simultaneously there’s an underlying gravity throughout the works. Anyway, what’s your answer to Waiting for Godot or Endgame? What about Joyce or Beckett? :p
P.S. I can’t figure out how to message you privately, so I’m forced to do it this way.