Seven delivered on the open world, sidequests, and character....
FF10 could've had all three but it lacked true open world and it was corridor after corridor (done better than FF13 of course). To me this game has the best limit break system of any rpg.
FF 8 is a strong contender, due to the fukked up story of child soldiers who are given GF's which causes them to suffer from amnesia....literally the perfect soldier program. However, very little minigames one of which was a very annoying card game, stops it from being the GOAT for me....well that and the limit break system.