The free training and an excellent progressive maintenance deal are naturally attractive incentives.
Prices between the two competitors are actually fairly close on these single-aisle aircraft and while both manufacturers will sell these models at below list, the amount of the discount is kept confidential, making it difficult to truly judge who paid what amount for x number of frames.
Passengers seem to appreciate the A320 series cabin - the IFE screens on the Airbus are a hit according to industry surveys.