10086sunset said: "If those are your two choices, I would watch the films first and see which better appeals to your sensibilities...
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Actually most of the people that I have met who loved the movie Waitress were lesser fans of the musical. I think when you get attached to one format, switching is not so easy. I would rather go in cold.
I personally didn't care for School of Rock the movie but loved the show (and I haven't seen the Waitress movie).