@Mix Android / @Hendrik Peter
I've enjoyed coc.nvim, but I've had lots of trouble trying to get the Python plugin up and running (on either MacOS or Linux). I was also frustrated at the number of 'X is not a function'-type errors, which are kind of a smell.
YCM is much older, and instead of having a bazillion plugins they just have one repository that supports tons of languages (including Rust).
I want to love coc.nvim, but I think YCM is more mature and probably what I need right now. Plus it works out of the box with no extra config, my only vimrc changes are two keyboard shortcuts.