Which story is more "tragic"? Oedipus the King, Metamorphosis, Hamlet

Aristotle essentially defines Greek tragic structure via Oedipus, so I think it pretty much has to be that one. Metamorphosis doesn’t involve a fall from greatness (Gregor is pretty low to begin), so I don’t think it qualifies as a classical tragedy. Hamlet is too navel gazing. Also, I’m not sure if he has a clear enough fatal flaw. Is he too introspective, too moody, too unwilling to take action? Yet it is in the moment of greatest action that he dies. Hamlet is almost the beginning of a new theatrical form, and I don’t think it a classical tragedy either.

Oedipus absolutely has all the qualities of Greek tragedy (again, by fiat, since tragedy is defined around it). So I agree with your take on the question.

Is it really meaningful to try to compare the degree of tragedy, as if it were a single measure?

oedipus most embodies the definition of tragedy as i understand it. a hero who is undone by events beyond his control and consequently suffers a fall from grace. not so for gregor samsa. hamlet is a tragedy, but with more nuance than oedipus

i say lamlet

I would argue Hamlet. Had Ophelia but known how to swim . . .