Both great choices, obviously, and a very subjective question. I have and love both. I feel MB is the better for the following:
Theme integration is outstanding. The Warner bros. oversight is obvious in the quality.
Every aspect of the audio is flawless. The voices are movie quality voice-overs, all call outs are in consistent voices and not random like . The music is perfectly matched to the theme and never gets old. The LCD animations in color are great. The CD in the middle is dated but the playfield artwork is otherwise great ad the cabinet beautiful. The cabinet on MM is lackluster.
I feel like the climax of MB builds longer and is more satisfying when you reach it than MM which feels flat by comparison to MM.