Generally, which uses more battery? WiFi or Data

I have an HTC One X running right out of the box on AT&T. I am trying to figure out if it's better for my battery to have the WiFi on while available or if it's better to use mobile data. Just for when the phone is just idling, because once I start using it I switch to WiFi if possible.

tl;dr Which uses more battery, WiFi or Data?

Edit: Using 4G