I don't see how anyone can vote before seeing the final showdown !
Fantasia has been strong throughout the competition, and has never hit a sour note. She's also obviously the judge's favorite (and my pick of the two who are left).
On the other hand, Diana has been gaining momentum in the last few weeks. She might really step up to the plate and win over the public.
In the last poll I saw, when it was down to the last 3, when asked who should go home that week, most people chose Jasmine (rightly so), but more chose Fantasia than Diana.