More specifically then the general title, what editor (or IDE) do you use, and for what languages. Why do you use this editor, and what features does it give?
I am most interested in Python, Ruby, and Javascript.
I currently use Aptana for javascript editing. It gives me a nice editor (I like eclipse editor), a 1/2 useful outline, sometimes actually does auto-completion of variables instead of me having to type it all out, A pretty decent code formatter, and a tad bit of syntax errors as you type. However I am not a big fan of it, it has a bunch of features but its more of a jack of all trades master of none editor. Most features are incomplete at best.
I guess just three main reasons:
1) I am a very visual person, and like to see the project hierarchy. I like to click the file I want, instead of just using my keyboard. I know this flies in the face of the purist Emacs and Vim users, but I'm only about half hacker, and I like my clickey click.
2) I like the tabs at the top (as opposed to buffers that you can't see). I like to see the group of files I'm currently working with.
3) I like the Aptana plug-in, which does nice mark-up of HTML, Javascript, etc. It makes Eclipse a fairly nice web coding editor. I also like Pydev. So Eclipse supports all my favorite languages.
I do wish Eclipse were faster and stripped of many of its components. Also, I do use the command line for things like SVN and running commands in the terminal like "python manage.py runserver." But I like Eclipse as an editor.
Maybe it's just because Eclipse is what I'm used to. I suspect that is the root of all preference.