Originally Posted by mikeef

The economics of aircraft purchases drive all decisions. Forgetting about those companies that merged and got different types, airlines know what the projected costs of a particular aircraft are. They let the manufacturer beat each other up, in terms of discounts, maintenance, etc. Obviously, if you are a Boeing (Airbus) carrier and considering Airbus (Boeing) aircraft, the challenger is going to have to offer more discounts.

This article in the WSJ is 12 years old, but the fact that I remember it shows you how comprehensive it is. Not everything in it applies now, but it's a good basis:

http://www.wsj.com/articles/SB1047243854826319840

Mike