RubyMine is an Interactive Development Environment, not a Language Server Protocol. RubyMine doesn't need to use an LSP since it has all the features an LSP offers (and more) built into to the environment.
I used solargraph for a really long time and it mostly suited all my needs, but I've seen it chew through memory in resource-bound environments (laptops with > 8GB RAM). Solargraph is very mature and is actively developed as of today. I'd say it's still a very fine choice for anyone needing some LSP features in a text editor.
Personally, I switched to ruby-lsp some time back and haven't needed anything else but my requirements aren't the norm. I spend a lot of time in a terminal with tmux, vim/helix (which has ootb support for solargraph), and a handful of monitoring tools.
Overall, I would say solargraph should fit the bill for most users. Ruby-LSP is great if solargraph isn't cutting it for you in some way.
when i want to use end_with? method, both LSP don't show any method for the word variable. do you know why is this happen? i also use neovim with coc.nvim for the LSP plugin. thanks for the reply btw :)
Interesting. I've had this issue before and I've concluded that both LSP gems don't really have a great solution to this problem. It crops up for me in both some code blocks and nested blocks. The solargraph maintainers have provided a solution for user-defined Classes here, but that's not really applicable in your case.
Being frank, I would open an issue with both LSPs with your code example to get a better idea of what's actually going on here and what potential solutions you can explore. Sorry I couldn't offer more insight here