Texpad (https://www.texpadapp.com) most often; I like the editor, it has syntax highlighting and shortcuts. You can set it to auto-typeset as you type and it can sync the PDF with where you are in your TeX file. I use Overleaf (https://www.overleaf.com/) when I'm collaborating with others.

Atom (https://atom.io/) and Sublime Text (http://www.sublimetext.com) will have plenty of packages that you can install to make it more IDE-like.