I know PhpStorm is a little difficult to get into, but I can't overstate its ability to spot errors for you. Not only is it unbelievably good at warning you about subtle PHP syntax and usage errors, but if you make a full MODX install into a project (which you can do with a couple of clicks) and do your work inside it, PhpStorm knows all the MODX classes and their methods.
It will catch misspellings, missing required arguments, using return values from methods that don't return a value, and much more. It will also prompt you with the arguments you need to use for any MODX method or function based on the PhpDoc comments in the MODX code.
I just solved a problem in an hour that would probably have taken me two weeks to find if I hadn't been able to step through the MODX processor code while running from the Manager in the PhpStorm Debugger. PhpStorm 9 now shows you the values of each variable in color right in the code as it steps through.
Maybe Atom can do all that, but I seriously doubt it.
It's not a religious issue for me, I just want to make people aware of what it can do.