Honestly I think that autocompletion gets in the way more often than it actually helps. To me it falls in the same realm as autocorrect on phones, well meaning but wrong often enough that I turn it off before I throw my phone out a window.
The thing is that Ruby is a straightforward enough language that often times you won’t need the tooling. Java, on the other hand, thrives on being a cryptic pile of noun-based mayhem that requires an IDE to have a prayer of understanding what madness has happened there. If your language of choice requires an IDE to get anything done, you should really be reconsidering that language.
As to why I tend to use Vim
It forces me to actually get to know the language, read through the syntax, and actually understand what’s going on. I only ever make autocompletion, macros, and snippets whenever I know what I’m doing so my editor evolves organically as I do in a language. The newer I am to and the less I use a language, the less I should touch fancy tools which abstract me from learning it better. The earned productivity is well worth the initial uphill.
Combine that with vim-slime and tmux and I effectively have all the features you could want out of something like Lighttable and other REPL heavy development cycles. I’ve heard there are cleaner ways to do this in Emacs, but I haven’t had a good enough block of time to critically evaluate that.
Why I use Sublime
Because I fear for my life pair programming with those not so vim-inclined 