GHoST_18 SG i think 9 is the easiest to play.... and also the lousier among the series.. 7 was the best imo...
SpeedStar SG I never play vi but i believe it should be the best out of all the series in ff. But if i want to rate those which i played, 7 will be the best. It has a nice story and also the cool guardian they have...etc, knights of round table.
skyfoo SG played 8 and 9, 7 only touch abit. 7 for its minigame, still rmb the arcade and the chocobo race. 8 for its story. 9 dun stand out in anyway except its cartoonish nature.