I also prefer the CFM, but I agree that the IAE is most probably a bit more modern. It uses a lot less oil - with fuel I cannot see a difference.
Something strange from a pilots point of view, is how the spooling up and down is programmed on the IAE. Sometimes you undershoot speeds by 10 kts or more after a level off. I never saw that on a CFM Airbus. Since this characteristic has nothing to do with engine, I guess it's a software programming problem. Cranking during start-up has been significantly reduced with the younger IAEs. It's 30 seconds now like on a CFM.
I think there is also a price difference between the two, IAEs lower, that's why everyone is ordering them now, especially the LCC.
Dani