Converting MXF to H264 or H265 - best settings (max quality/min storage)

Hi,

I'm a freelance editor and have a ton of raw footage in MXF format stored - some in 1080p, some in 4K.

I want to free up space on my drive, as these raw MXF files are quite space intensive, but I don't want to delete the files or lose a ton of quality (in case, for some reason, I need to revisit some old project later).

So what I want to do is convert these raw files to h264 or h265 or something that will get as close as possible to the original quality, while still freeing up some disk space.