It depends on how prepared you are for the September LSAT. Taking the September LSAT will give you better opportunities at obtaining scholarships, but those opportunities are lost if you are unprepared for the test and score lower than you may have if you wait until December. If you feel you are scoring consistently on practice tests and that further study will not result in an increased score, then take the September test. If you feel that additional studying will result in a higher score, then I suggest waiting until December.