I switched from Sublime 2 to Atom earlier this year and haven't really looked back. I admit, though, that my customization needs in the environment have been minimal. I've written a couple of editing short-cuts for Elixir source, but that's it.
I'm curious to learn what features in Sublime merit purchasing it over Atom or another free text editor.
Nothing in ST3 annoys me enough to push me away. Nothing elsewhere looks good enough to pull me in.
I've been somewhat curious about Atom lately, especially when I dealt with how slow stylelint was when linting through Sublime (1s+...), whereas Atom doesn't have this problem because it already runs a Node process, but really there haven't been any real impetuses to switch to another editor.
If I were deciding between the two without owning Sublime, I'd probably go with Atom first because it's free, then if I found it to be lacking, be it through customization, plugins (if I liked Python over Node for plugin writing, for example), or speed, I would probably go with Sublime.
Sublime has what I need and it's quicker to start. I don't need something that I can customise with CSS, I need a fast text editor with syntax-highlighting.
On a plus-note, I have just convinced myself to use Vim with the following options: set number, set mouse=a, set colorscheme evening and syntax enable
I frequently look at trace files that are sometimes 100MB+ in size. Of course, I don't read all 100MB+ of the file, but that's where I have to start. Normally you'd use a viewer, not an editor, for this, but I also like to annotate the trace files as I work through them.
ST3 works decently with these files, so I keep sticking with it.
Also, I don't think that it is a good idea to implement CPU intensive real-time applications in javascript (e.g. code parsing or syntax highlighting). There are plenty of languages/tools that suit well for it, there was no reason to pick a javascript as the primary language for a editor.
Away from the speed thing (which is definitely noticeable on my two year old box), and from non power user perspective, I'd say they are pretty close to equivalent.
Note I also use VS Code a lot because its Git Diff view is awesome and its debugger is a rock too. The extensions are generally not great though.
And I use vim when I need to edit a single file quickly.
Add to that the fact that I often need to edit text on remote machines via ssh and it just wasn't worth it to me to keep using it when Vim was (and still is) perfectly satisfactory.
Actually, the only thing I really want from Atom in sublime is to provide a pane that can embed Chromium.
That will give me pretty much all I want to write useful extensions.