i gotta be honest, i LOVE both but movie is better objectively.
the thing with the heathers musical is that its a musical, meaning you are only expected to see it once, meaning they have to be really obvious about whats happening in the story and doesnt leave any room for subtext at all. also i dont like how they woobified JD in the musical tbh....
STILL i LOVE the musical but the movie just does a lot of things better, jd's characterization, the ending, heather duke, the dialogue n the costumes