Runtwer

This method is decent but can be improved significantly. All you want to do is kill the heartless outside the door at the top of shack, drop down to the left side and kill the ones that spawn at the door to the seashore. Turn around and work your way to the bottom door of the shack and kill the heartless that spawn on the beach. Run inside the shack, go to the top and back out. Rinse and repeat. You'll kill much more enemies in far less time. If you do the method listed and clear the whole island, you have to fight across bridges where you can fall and have to backtrack in order to get back to where you were, enemies can fall off as well. You have ladders that you have to climb or obstacles to jump over and then you have to run all the way back from Tidus's area to the shack in order to respawn the enemies. Such a HUGE waste of time when you can simply do a much much smaller loop and respawn the enemies quicker. You'll shave off a lot of time. Clearing the whole island is just...stupid.