Final Fantasy XII. Now it's not the worst one, but after playing it I was convinced that the series, experimental as it is, should more or less be a series of traditional JRPGs. What made the best age of the series great was experimentation with the kinds of stories being told, as well as experimentation with system mechanics within a given, somewhat strict systematic framework.
Think of it this way: the difference between any of the games between Final Fantasy and Final Fantasy X was like the difference between the different Street Fighter series. The difference between XII and XIII is like the difference between Ultimate Marvel Vs. Capcom 3 and Samurai Showdown V Special.
That said, I wouldn't want it to be as strict as it is with the Dragon Quest games. That's like the difference between Street Fighter II: The World Warrior and Street Fighter II: Champion Edition.
Think of it this way: the difference between any of the games between Final Fantasy and Final Fantasy X was like the difference between the different Street Fighter series. The difference between XII and XIII is like the difference between Ultimate Marvel Vs. Capcom 3 and Samurai Showdown V Special.
That said, I wouldn't want it to be as strict as it is with the Dragon Quest games. That's like the difference between Street Fighter II: The World Warrior and Street Fighter II: Champion Edition.