Eh I don't know. If you had asked me as a kid I would have said Sky easily but after playing all the games again I gotta say Sky has some really hindering flaws in what everyone proclaims are the best parts of it. There's a lot of things about it, even in the Special Episodes, that don't make a whole lot of sense when applied to the larger timeline of the game. I think Sky had the best final bosses, but I think PSMD had the best storyline of the group.