I've seen both films.
I loved The Simpsons Movie. I hated Transformers.
Which was odd, because I was expecting to love Transformers and be disappointed by The Simpsons.
The Simpsons Movie was genuinely funny, touching, had a decent storyline, and there was a really good atmosphere amongst the audience. Everyone was laughing, a good time was had by all, and the humour was much more in keeping with the earlier, funnier seasons of the show.
Transformers was a huge disappointmnt. It's a Michael Bay film, so clearly the effects were brilliant. But the storyline was utter garbage, and the script was truly dreadful. After the opening action sequence there's about 30 minutes of non-action, and the dialogue in this portion was so awful, so cringeworthy, that I felt really quite uncomfortable. The characters have no depth whatsoever, and so subsequently I found myself not caring about the fates of the humans or the robots. By halfway through the film I was utterly bored. And it's not like I don't enjoy action films. I went in fully prepared for non-stop action, but it just didn't hold my attention at all.