For dealing with Flexible Image Transport System (FITS) files, both languages have dedicated packages: Astropy for Python and FITSIO for Julia.

I prefer Astropy personally, but here are some things to consider.

1. Libraries and Tools: Python's Astropy is a mature and comprehensive library with extensive community support, and it provides a broad range of astronomy-related functionalities, not limited to just FITS file manipulation. On the other hand, Julia's FITSIO is more specific, primarily focused on reading and writing FITS files. Its scope is narrower than Astropy, but it is well-optimized for its purpose.

2. Performance: Julia, as a language, tends to have better performance than Python due to its JIT compilation feature. This could lead to better performance in data-intensive tasks such as handling large FITS files.

3. Community and Support: Python has a larger user base and more extensive community support than Julia, especially in the field of astronomy. This means that it may be easier to find resources, tutorials, and solutions to potential issues in Python than in Julia.

Since I used Astropy, I wrote a guide for you with some common commands I use: