i am thinking in terms of good looking pictures, and how large the pictures are, because i like to be able to make my pictures big enough to have a a desktop background.
iPhone 4s: 8MP camera, 1080p 30 frames per second video on the back camera, VGA quality camera and 30 frames per second video on the front-facing camera
Evo: 8MP back camera, 1.3 MP front-facing
I would suggest the iPhone, I LOVE the camera on mine; it includes cropping, red-eye, and auto-enhance right after you take a photo.