AIRBUS A320 FAMILY CAN BE POWERED BY EITHER OF THE BELOW ENGINES:
CFM 56 SERIES,IAE-V2500-A1/A5/A7 SERIES OR THE PW - 4000 SERIES DEPENDING ON THE OVERALL USEAGE OR SELECTION BY THE CUSTOMER.
YES AS MENTIONED IN EARLIER POST THE CFM ARE BETTER IN START TIMES,REALIBILITY ETC AS COMPAIRED TO OLDER V-2500 SERIES , BUT HOWEVER EVERY ENGINE MANUFACTURE HAS A CERTIAN ENGINE ANALYSIS CHART RELATED TO TYPE OF OPS CAPABLE IE ETOPS, IN FLIGHT ENGINE SHUT DOWN RATE OVER THE PAS XXX YEARS, ENGINE TROUBLE ENCOUNTERED FOR THAT KIND OF ENG. ETC AND THEN IF ONE COMPAIRS THE OVERALL PERF OF EACH TYPE CFM/PW/IAE..a customer can select its choice of engine to its type of airframe chosen in the A320 family... guess that y we have diff airlines/regions use diff engine for the same a320 family airframe.
then again the reasons for actually choosing a given engine can be based on many pther reasons, but gegerally its Performance Based..