See everyone above saying "I prefer A because..." or "I prefer B because...". Ignore it, it is meaningless. I really doubt anyone has ever read Starship troopers and said "Well this book is O.K. but it would be so much better if the Terran federation was the USA!" or read the Worldwar Tetralogy and thought "If only this was taking place on Capricorn Beta 5." Go with what you feel works best in the context of the story, and what you're more capable of writing. It's likely one of the two choices will mesh better with the plot and your abilities but none of us here have any real idea what the plot is, and (Unless you've posted a bunch of stories previously) nor your writing style. In the end as long as the work is genuinely enjoyable to read, no one will really give a damn if the world your using is that of reality's or one of utter fiction.