I liked The Simpsons better but since the same ride vehicle is used, I still can't ride it. I'm 6'2" and my head always gets banged around in the back so I stay away from it. I rode The Simpsons during the passholder preview last summer but haven't since.
BTTF was definitely a rockier ride than the Simpsons. However, I can't commit myself to which is better because I like(d) them both. Maybe I need to ride the BTTF ride at Universal Studios Japan for comparison. When I win the lottery.