Using a good text editor during development is very important, as it can ease the job. There are two powerful and old text editor: Vim and Emacs. They can handle large files, split window, indent smartly, highlight syntax, work in console (without GUI). However, both text editors have steep learning curve. Users have to memorize a lot of hotkeys if possible.
My primary text editor is jEdit. It also provides approximately unlimited window splitting. jEdit can also installed with multiple plugins. Users can also create their own macro script using Java language. And it is cross platform. Similar to jEdit, Kate also works with window splitting.
Atom seems like a very promising text editor. However, the current stage has a limitation. Atom now cannot handle session. It does not reopen all the files opened in the previous session. There are some packages related to the session, yet none of them works. Besides that, open recent file is available only through the packages.
Hopefully Atom will keep improving. It is full of potentiality.