With the Simpsons, it's replacing an old franchise that most kids today and possibly even some of today's adults may never heard of. As great as BttF was in the movies, the ride was good, but not that great.
I haven't been on the Simpsons yet, but the franchise has weathered the tests of time. Sure, some hardcore fans say that the show isn't funny anymore. But there are fans that still appreciate the show, like myself. The show has changed and so have I. Not everything on the show is great, but it has its moments.
With Stitch, it replaced a generic ride. I'm not saying that it's a good move, but there was almost nothing attached to the ride. It wasn't as memorable as It's A Small World, or Space Mountain. Neither ride was originally attached to any Disney Characters.
Honestly, I didn't think BttF was an awesome ride to begin with. It was great when it was first around, but it began to show its age quickly.
Which one is better is all going to depend on the person. I think fans of the Simpsons will love the ride and it was great to be immersed in all things Simpsons. If you don't like the Simpsons you may not be to into it, though if you are a themepark fan in general it is great to see all the homages to themepark fare. Now did anyone else besides me see the BTTF reference during the ride when you're in the Springfield "town square." I swear I did and I sceamed it while on the ride. I'll have to go on again. Yes it uses the same ride mechanism as BTTF but some surprising additions that i liked. Plus I liked the fact that I was not in pain when I got off the ride. My last BTTF experience had me a little sore.
As for TSMM, I think this is an awesome ride for families and those looking to have a good time. I kept thinking the whole time that my mom would love this ride. She does not to big coasters, or anything with sudden drops. I think the only coaster ride she will even step foot on is BTM. She'll do white water rides and simulators, but she doesn't like the Simpsons. haha
Anyway back to TSMM, the only people who may not enjoy it are those that are strictly thrill seekers. This is not a thrill ride in any shape of the imagination. Though I do enjoy the ride in between games with the cars moving around and to be honest I kind of got lost as to where we were going. I think gamers will get a kick out of the interaction part of the ride, trying to beat the high score.
So when you come to Orlando check out these two great attractions, it will be interesting what comes over the next few years with Harry Potter, and I'm sure Disney's got something up there sleeve in response to that. :)
However, I concur with Ted and others, and voted for the attraction that was actually brand new and not a re-engineer.
Although Toy Story's new technology is exciting, it's another new screen-based attraction for Disney. Not that The Simpsons isn't one, but it's also replacing one.