I think alot of Diana's weaker performances earlier on were the weeks she was fighting off the cold/sore throat her, Jasmine, and George battled. My 2cents:
Diana - Powerful voice, yet as she shown tues, can tone it down and soften things up... great raw performing ability... yes, she is still 16.. but has good stage presence already. Works well with the crowd, and seems comfortable on stage. I see her as highly marketable in multiple markets, including tv/movies. Her cute bubbly personality will work well.
Fantasia - I personally don't care for the tone of her voice in most songs.. too nasally/maci gray-ish... but she is a good performer, and does add her own flavor to each song... which is a good thing. She is unique, which isn't a bad thing, BUT it can limit her marketability... I kind of see Fantasia in the same light that I saw Ruben.... and trust me, I saw him in concert in LA a few months ago..and he was TERRIBLE!! The first couple songs were good, but after that he sucked! Raspy, out of breath, and no versitility at all. All the songs sounded the same... My wife and I both agreed..it was the LAST we would ever pay to see him.
I would be comfortable with either of the girls winning... I'm leaning more towards Diana, but the bottom line is.... my vote will go to who earns it next week!