In all honesty before I go back to Vector I like leveling in the cave to the sealed gate. It gives good xp 555-700. Good for the time you do it and you can prepare locke and terra for the battles awaiting them while they are alone in thamasa. Once Kefka and Gestahl go after the statues I like to just head straight for the floating continent where I do the rest of my leveling (If I feel any is necessary).