Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance -- Special Report 286
Anyone that is still confused should read this thoroughly as it explains answers more completely then mentioned here. IF you read this completely you can make an informed decision about rolling resistance and tires. I tried to cover everything here that was in the study, but it seems to be ignored.
And to answer someones question about the most efficient tire: Bridgestone 381 (It is a 14 inch tire).