Personally, I'm not too sure. I always thought that he was being sincere because his tone of voice and facial expressions were different to when he manipulated the genie into getting them out of the cave and when he tricked Jafar into wishing he was a genie. But, I know that the filmmakers said that whenever Aladdin lied while dressed as Prince Ali, the feather on his hat would sway and fall over a little. The last time I watched the movie (a week or two ago) the feather sorta fell over, but I couldn't tell whether it was because of the way he was moving or because he was lying.

I think it could be read either way. On one hand, it was just an excuse he came up at the moment to throw her off guard (since Jasmine almost caught up his conversation with the Genie), but he seemed pretty defeated at that point, ready to give up his fruitless efforts to woo Jasmine.

^Well said, I agree. He did seem defeated and willing to give up.

I think he meant what he said but said it so she would care more when he jumped the balcony so it was a bit manipulative so I guess I could have voted that as well.

What scarletunicorn said.

I agree with scarletunicorn.

I personally believe that it was a mixture of both. He really did seem to understand that treating her as a "prize to be won" was uncalled for. But at the same time, he seemed to say it out loud so that Jasmine would know that he understands where she's coming from and so she'd be impressed and give him another chance.

^Same... I do think he believed it, but I think at that moment he was just saying it because its what Jasmine wanted to here.

I agree that it's both. He probably meant what he said (even earlier, he said that she "deserves a prince"), but he may have said it so as to make her think he wasn't all that bad.