Not a fan of Atom. It seems a bit sluggish and it's configuration interface is... lacking... in many ways (come on, if you're going to have a GUI-ish config interface, at least provide a pop-up font menu to set your editor font, or, at the very least, display what the current font is).
Sublime is blazing fast and its speed does help compensate for some of its shortcomings in other areas (which may or may not be shortcomings in your opinion -- a lot of this is a matter of personal taste).
If you don't want to use Sublime as a Python editor, I'd look at Komodo Edit. It's also free and open source, actually has a usable configuration UI, is scriptable in Python (a la Sublime), has a minimap, etc. It's not as fast as Sublime, but it is faster than Atom (though not as fast as Sublime) and between Atom and Komodo, I'd definitely pick Komodo.
Between Sublime and Komodo, it's a trickier decision as both are great editors IMHO with their own strengths and weaknesses. Sublime wins for speed, some of the really cool features with it's keyboard-based UI, and the great plugin community/selection. Komodo wins for price (free), open source (if that matters to you), and configuration UI (while I like the idea of plain text configuration files and have no problem with the JSON syntax for them, I still think a proper config UI is a good thing to have in addition to just editing the config files directly). Komodo also has some configuration settings that Sublime (at least out of the box -- perhaps the added functionality is available via plugin) lacks.