Cook is a classic and the original.
Chenoweth has yet to prove herself as a real interpreter on songs.
She's funny as hell, but she does lack in the vulnerability. She's yet to show her versatility role wise. They've all been cute funny blondes.
Cook is the original ingenue. Of course, I've never seen her, but even in her recordings she has such a genuine understanding of the songs that shines through.
While I do love Kristin, I must say Cook until further evidence is presented.
Personally, I think I have too much bloom.