TLDW: Atom looks really good.
I’m currently using Sublime Edit (http://www.sublimetext.com/) which is also really good.
Atom could take Sublime’s role on my quick launch bar if it had one killer (for me) feature.
Yes, Atom does have an auto complete plugin : https://atom.io/packages/autocomplete-plus, but - its dependent on the current project and or snipits.
Sublime, via Komodo has a autocomplete system called “CodeIntel”. Its great : https://github.com/SublimeCodeIntel/SublimeCodeIntel does all sorts of smart things like :
var fs = require('fs');
Will know that fs is the filesystem lib and give you the auto complete for its functions.
Once Atom has something similar, or i work out how to make autocomplete-plus work in this way, i might give Atom another try.