The whole Atom vs Sublime Text discussion is interesting, but the bottom line is that they both will be more than good for editing tf2 configs. Overkill even, compared to Notepad++
1. Atom is free, Sublime is Winrar Free (you get a rare popup asking you to upgrade).
2. Sublime has the bigger community with more easily found information about it
3. Sublime has far better performance.
4. Atom has likely more customization, as it is a open sourced project and advertised as totally hackable.
5. Atom has nice little features in its UI that make life easier.