VI is pretty easy. Although a beginner might not know all the abusable tricks in the game, so..

VII isn't too hard at all. Maybe get him on that.

VIII's system might overwhelm a beginning player, hold off on that until later.

IX is simple enough, and enjoyable. And it's the perfect FF experience. I'd definitely recommend it.

X may also confuse, but not as much as VIII.

Overall, I'd recommend IX for the beginning player, a perfect choice. If not that, then probably VII. (Unless they complain about graphics or some other foolish thing...)