I'd expect C to run the best due to it being compiled. JS is pretty quick, but we're talking a microcontroller, so any speed you can pickup by reducing computation cycles is a win.
Easiest/better is using what you already know as that'll provide the best speed to MVP. If it's too slow in Python/JS, but it seems like a useful thing, it's probably worth rolling up your sleeves and learning some C. At least enough to build a python library.
I'd expect C to run the best due to it being compiled. JS is pretty quick, but we're talking a microcontroller, so any speed you can pickup by reducing computation cycles is a win.
Easiest/better is using what you already know as that'll provide the best speed to MVP. If it's too slow in Python/JS, but it seems like a useful thing, it's probably worth rolling up your sleeves and learning some C. At least enough to build a python library.