For me it's Django. It's a mature framework but also gives you plenty of ways to customize and configure for your usecase.

However, another might be the libraries. If you have to implement machine learning or data analysis on your backend, you would probably be better suited with Python. There are also probably other of examples of this too. Python is a more mature language on the backend so I would guess it has a bigger ecosystem there.

I think out of the box JS is more performant. However, you can make Python good enough.