After watching Razor I am convinced the final cylon is Cain. Besides the fact that they went thru the trouble of bringing that character back and expanding upon her, they also included a very peculiar scene when that oldtime cylon didn't shoot or take youthful-Cain captive when she fled from her sister with the teddy bear, it absolutely revealed to me that she is the last cylon. That is why that cylon didn't shoot or take her. Cylons know which humans are really not human otherwise they would just shoot everyone that doesn't look like a heap of metal.She would be the best choice as the last cylon and a blast to watch her lead the cylons against Adama and the humans...
..Oh the irony