I used to use YouCompleteMe with Vim, then switched to deoplete on Neovim, because deoplete was easier to extend without having to maintain a fork and the user experience was pretty much the same.

I briefly tried out Coc but didn't find it to deliver anything compelling to make me switch away from a relatively fine-tuned deoplete-powered set-up (along with UltiSnips, LanguageClient-neovim, and javascript-typescript-stdio etc). I like the fact that there is competition though and an LSP ecosystem that's getting more and more robust all the time. We finally have multiple high-quality options to bring IDE-like features to Vim.

Let me tell you why coc.nvim is created.

I used to use deoplete.nvim, LanguageClient-neovim with javascript-typescript-stdio, but they easily broken lots of time everyday and debug the problems is also quite challenging. So I made it to be able to load fork of vscode extension, and coc-tsserver implemented more than 95% features that vscode could provide. It's not easier to switch vim plugins, consider come back when you would like to try out some new features.

YouCompleteMe is hopelessly slow even on a beefy computer with a medium-sized code repo, despite configuring and optimizing. It's simply too painful to use. deoplete is significantly faster, but also becomes painfully slow when you have a few hundred files and a few hundred thousand lines of code total.

I'll try Coc; hopefully it's fast enough. IntelliSense works great in VS.

I use TabNine and it's been pretty amazing.

Do you know how it compares to YouCompleteMe or Coc.vim? Is there something it can do, which the others can't? Do you feel that the suggestions are better? something else?

I haven't had time to try those two yet. I believe TabNine uses YouCompleteMe internally. There's a discussion here: https://news.ycombinator.com/item?id=18393364

TabNine's selling point (literally, it's $49) is that it uses machine learning to provide completions without having to configure any sort of knowledge about the language you're using.

I'd like to see such a comparison too. I've been considering switching to YouCompleteMe from ctags/cscope, but this looks like it might be even nicer, especially since a number of my teammates already use Intellisense with other editors.