The root DB user is all I ever use when developing locally, regardless of which local server I am using, Windows and Mac.
Unless you have some very specific reason to use one of your own creation, perhaps consider just doing the same :-)
If you are concerned about how using the root DB user will affect things when you move the site to a web host, don't worry, it will not be an issue. I have moved literally 100's of WP (and other scripts) from local to live (or other local servers) and have never had any issues in this regard.