I would have to go with Final Fantasy 10 for a great storyline-and Tidus is a sports star that narrates this story, and he is from the futuristic metropolis called Zanarkand. Tidus gets involved with Yuna on her journey to save the world-and they make a journey trying get back to Zanarkand, while trying to save the world of Spira-which is quite corrupt.
I have much preference to a storyline that have save the world plot and in my opinion, it's in Final Fantasy X that this storyline was evident completely. So that is my best Final Fantasy series storyline that rocks very well.
I think my favorite is going to be Final Fantasy 6, even though I'm aware that some gamers wouldn't appreciate the game for one reason or another but it's still my favorite no minding anyone's opinion. I also love the storyline of Final Fantasy 14 and still haven't made up my mind about the FF 15 version.