FFIV or FFVI?...hmm...I guess I'll have to go with FFIV, even though VI is my second choice. The story of Cecil and his companions is a great story to behold. With great plot twists you can't really understand what could happen next, but it always could.
ex.
When Yang, Rydia, and Edward fall into the ocean when Leviathan attacked
their boat, but then later in the game, they show up. The most suprising is Rydia
when she saves them from that elf that adds magnets around his cave, making it
impossible to defeat him, and eventually they all fall, but an Adult Rydia comes along
and saves them, I was so happy.
The only thing I did not like about it was the easy battles, I pretty much destroyed all of the bosses with maybe dying once or twice.
The music really makes you dwell into this world as well. The music fits the transportation type if you are in a Boat or Airship. It also fits in the battles. Even if it might be a bit of the same music, it still gives me the aggresion needed to battle these enemies. Though both VI and XII were two of the best FF games I've ever played (And trust me, I've played all of them...except tactics >_< Can't find a copy) I still love FFIV the most, and I cannot wait until the remake of it for the DS. If it's anything like FFIII, then it's bound to be good.