I can tell you what a neutral accent is... I'm a midwestern American, born and raised. I recently was in Dubai and had the pleasure of meeting some of our pilot colleagues from all over the world.
In fact, out of the 14 of us, at least 12 spoke impeccable English to the point that, sight unseen, they may as well have grown up in the U.S.A. My favorite guy, that I spent all day with, was from the Sultanate of Brunei (sp?) and his English was so great we talked all day.
Outside of a few idioms, he had it all. We even had a good old fashioned, all-American fist-bump at the end.
