Another Atom user!
Molly101
54chi
Oxyrus
I use Sublime Text, however I’m trying to get used to Vim, since it looks really nice and feels good!
3
Calamitous
Mandemus
I happened to notice that the IntelliJ Elixir plugin by Luke Imhoff has been getting a flurry of activity as of late.
2
john
greyhwndz
dgamidov
I have started to use free Visual Studio Code.
There is Marketplace with lots of extensions.
It supports Mac OS, Linux, Windows.
Elixir extension has syntax highlighting and snippets. It is not enough, but may be it will be imporved, because Python extension allows lot of different useful things 
3
skippednote
I’m a long time Vim user but for Elixir I tried out Atom and Spacemacs too.
Atom has been slow and crashes frequently. Spacemacs is good but I like staying inside the terminal (I know emacs has first class terminal support, but that doesn’t work for me).
I’ve settled for NeoVim with Alchemist.vim for completion and documentation with Deoplete. These are working pretty good for me as I learn elixir.
1