I have noticed in the US at least there seems to be more A320 series airlines with the V2500 engines. I fly Frontier quite a bit and notice they have the CFM's. To my knowledge US/HP and the upcoming Virgin America are the only others. I would imagine fuel economy may or may not be the answer but what are the main reasons for different carriers choosing the different engines on the A320 series?
I did a search and found results but none answered my question.