I would suggest vim
for any type of serious code development and/or debugging. There is a file called "tags" in your moodle/ directory that contains a list of sorted functions, variables, etc. that can be accessed directly if you're using vim. For instance, let's say your browsing code in your editor and come across a function, moodle_foo(), and you want to see its implementation. Move the cursor over the function and hit CTRL-], and you will jump directly to the function definition. You can then use CTRL-T to go back to where you were. This is only a very small fraction of the things you can do with vim...highly recommended! I've been using it (or a variant) for many years, and would never consider using another text editor for coding.