Screen comparison video: iPhone 4s vs. Lumia 900
I strongly favor AMOLED over LCD screens; especially if it's not a pentile display.
HTC One X, Nokia Lumia 900, Apple iPhone 4s screen comparison (via foxfire235)
Seeing the two displays next to one another I don't think there is any chance I would choose the iPhone, but it comes down to what you think is more important; reading text or looking at images and video on the phone. For my money the Lumia 900 is clearly the most vibrant and pleasing to look at.