The popularity for operations (popularity being what makes best sense money wise) goes in circles with new developments. IAEs on A320 family were always best before as they used less fuel than the CFMs but now the CFMs have become ALOT more economical than the IAEs so most operators with the A320 family are choosing to go CFM off the production line unless they have alreasy got an IAE only fleet of A320 family aircraft and want to keep commonality as that is cheaper than mixed.