Selecting the correct aircraft is a complex process, involving a multi-disciplinary team of people and skills with considerable knowledge of the business.  At a fundamental level, buying aircraft is necessary to support the basic strategy of the client. Typically, the aircraft will be purchased for either replacement or growth needs; replacement for when an aging aircraft begins to incur higher operating costs, or to introduce new technologies, whilst growth will trigger requirements for increased range, higher payloads and specific performance capabilities.


A key issue in appeal is that the airframe should be able to offer a good degree of flexibility for reconfiguration. Aircraft will be operated over a range of mission profiles by their owners during their useful lifetime. The evolving business,  personal requirements and tastes will dictate interior arrangement and the overall feel of a cabin, minimizing the complications for future reconfigurations and modifications  therefore becomes very important factor to consider.
Traditionally, aircraft selection decisions are dominated by the range capability of the products under evaluation. This was because range was often a limiting factor for clients wishing to expand their global reach. Today’s aircraft have much greater range capabilities and so this element has diminished in significance. The current offerings from today's manufacturers include products with a capability of over 7’500 nautical miles’ range. meaning that the vast majority of the world’s city-pairs can be served non-stop. 
However, many clients do continue to place the relevance of range when comparing aircraft types. There are sound reasons for this. For example, the future value of an aircraft is partly determined by its range ability. Operators of very early production models can often be disadvantaged, as take-off weights, and therefore range, are always limited until improvements can be worked into the design. It is very common  for the first version of a type offered with a conservative payload-range envelope. This is largely because the structural integrity of the airframe must be proven.
As experience with the airframe grows, so does the aircraft manufacturers confidence in releasing increases in take-off weight that had been retained as margins in the original structural design. During the life of the aircraft design in service, it is typical to expect several evolutions of the weight, each one enhancing the maximum range possible. Such developments are often accompanied by many other changes to the design as well, such as increased fuel volume and other product enhancements.
Using an aircraft with the maximum range may not be the most appropriate solution if that range is not strictly required. The same can be said for economics. Of course, it is in the interests of the client to minimize costs, but there are some additional considerations that can result in higher costs being incurred in order to ensure a better overall result in the longer term. 
The right economics will also be judged according to how forgiving the aircraft type will be in certain areas of the cost breakdown. For example, if a client will be using airports where landing fees are relatively high, then it will be important to place more emphasis on the take-off weight of the aircraft in the evaluation. Some aircraft types are more efficient, or productive, in terms of weight per unit of payload than others. 


Flexibility has become a key requirement - this is the challenge of matching a physically inflexible aircraft with an owners requirements that will experience constant change.
Airliners are able to offer a greater degree of flexibility. The large interior floor space and volume provide more opportunities in terms of interior layout, A key question is whether the inherent design of the cabin allows cost effective and rapid reconfiguration in order to address the clients future needs.
The issue of operational versatility can be seen from the perspective of the longer-term design, customers are now far more responsive to business and lifestyle changes than ever before, with re-configurations, and modifications of the cabin now commonplace.
Another aspect of flexibility that should be considered, is the degree to which the aircraft design offers alternative interior options. For example, it is always beneficial to be able to configure the aircraft for both private and commercial operations, different passenger counts and alternative interior layouts. 


Between the different airframe, engine and interior suppliers it is typical to expect different philosophies in design and maintenance, and different approaches to customer service and product support. Customers may pursue a multi-supplier philosophy for strategic reasons, such as spreading risk and encouraging more competitive offers from the manufacturers. Or in cases where competing manufacturers do not offer aircraft in every market category.
Following the decision to acquire a particular aircraft type, it can be beneficial to stick with that particular technology standard as the clients fleet develops. Besides the benefits derived from economies of scale and progression along the learning curve, there are synergies to be reaped in many aspects of the customization process, spares investment, tooling, training, and day-to-day operations.