I use gedit because it comes with Linux. I sure wish I could use Notepad++ without having to install WINE.
Any of them.
vi / vim
Just about any of them will work, just don't use a word processor. They don't handle plain text files very well unless you're careful.
You'll have vi or vim installed, but they are hard to use.
Which graphical editor is installed depends on your distribution. Could be mousepad, leafpad, kate, kwrite, or a bunch of others.
Whatever you use, you will either have to start it in superuser mode, or first make the configuration file writeable by all.
nano, vim, gedit, brackets, atom