Reimers, I am sorry about your friend.
If you're going to sell an airplane, you need to talk numbers - cost.
While the A320 and the 737 are in the same class, they are very different aircraft. The 737 easily beats the A320 on operating costs. Lower fuel consumption and lower maintenance costs as well as a longer design life (cycles). Why? Mainly because the 737 is lighter and simpler than the A320 with regards to fuel and maintenance costs. The relative simplicity of the 737 design also supports a proven dispatch reliability advantage. Airbus can (and frequently does) counter most of these advantages by offering better deals on initial purchase/lease coupled with enhanced maintenance agreements, bringing overall costs to nearly equal.
Fleet commonality is a huge consideration when a major airline chooses one type over the other. From the pilot's perspective, some like the fact that a 737 is a 'pilot's aircraft' - whatever that means (I've trained for both and found them both to be perfectly fine aeroplanes!) while Airbus counters with the fact their airplane is designed to be flown by pilots as well - including those candidates of whom English is not their first language.
Airbus also has the advantage of having an aircraft well positioned, by their ingenious FBW and automation designs, to mitigate the differing standard between the US and the EU on the minimum hours required to step into the cockpit of an airliner. The philosophy of the Airbus promotes safety through computerized protections and simplified systems management, while the 737's edge here is simplicity of design and proven concepts. Both are very safe, very capable aircraft and both have a history of minor design flaws that have since been corrected or mitigated through procedure changes.
I believe the Airbus has Boeing beat on cabin width, and most (at least in the US) operators choose to install better IFE equipment on the A320, giving the paying customers a better experience.
Then there's the difference up front where you've got a nice dinner/reading table in one and a hefty piece of metal between your legs on the other. Who's gonna be the better dance partner for your evening?
