A) Age (25) Although, she looks young to me.
B) Needing a winner who wasn't a white brunette.
Normally, I would say height, but please - they let Eva, 5'6.5 girl win! Technically, Eva doesn't even qualify for the competition.
Personally, I think Amanda's ANTM portfolio was way stronger than Eva and Yaya's combined. Although, that's from memory. Still, the fact that I actually remember most of Amanda's pictures and I remember nothing but a few of Eva and Yaya. And some of Amanda's post-ANTM photos ..