MPV, as it allowed a bunch of really nice custom upscaling functions and tricks (especially nice for animated films), though my custom config of that got borked on Apple silicon (probably using a wrong shader that only runs on the CPU or something like that, I just haven't bothered investigating much). Few cons – .config files only for settings, and it doesn't come signed.
IINA, as a more modern alternative to the above. Uses the same FOSS libraries, but comes signed and much more polished than MPV. Though recently it had some worrying developments with adding JS plugin support (nope, I don't need any JS feature creep in a fucking video player, no thanks).
iTunes or its modern equivalent (whatever is it called nowadays, as if I cared), as I still have a full library there.
Never warmed up to VLC, its UI was weird and had too many features I didn't need. Though it's certainly quite versatile, just not for me when all I want is to watch a single video file of a film.