I have been using LanguageClient-neovim[0]. It is great, the main difference I have observed between LanguageClient-neovim and coc.vim is that LanguageClient-neovim provides a more vim centered UX (e.g. it automatically populates location/quickfix list with errors, warnings and hints which enables quickly jumping between error locations) while coc.vim provides a great out-of-the box experience but feels like VSCode strapped to nvim (It has its own extension ecosystem based on VSCode extensions) - I greatly appreciate the effort by coc.vim's developer, he has done great work and coc.vim defiantly has its advantages[1] over LanguageClient-neovim. LanguageClient-neovim requires a lot of customization in order to fit it to your work flow but once it is done, the experience feels a lot more native. On the topic of which, LanguageClient-neovim feels lighter and faster to me and has the added advantage of being usable without any external dependencies (because it is a compiled binary). I highly recommend checking it out.
tl;dr:
coc.vim is for those looking for a VSCode like experience out of nvim (stuff works out of the box requiring minimal customization, installing plugins to get the required functionality) where LanguageClient-neovim is for those who prefer a vim centric approach (extremely minimal, manually customizing everything to get it to fit you workflow).
If you are interested in LanguageClient-neovim you can checkout my config[2][3] you might find it helpful .
[0] https://github.com/autozimu/LanguageClient-neovim
[1] It shows documentation for completion list items in a floating window similar to VSCode.
[2] https://github.com/L0stLink/anvil
[3] https://github.com/L0stLink/anvil/blob/master/settings/Langu...