Choose a charter aircraft by starting with the trip, not the aircraft. Most people do it the other way round. Starting with the trip is faster and cheaper, because limits make most of the decision for you.
Start with the airfield at both ends. Runway length, surface, landing aids and opening hours rule aircraft in or out before anything else. A short regional runway may rule out every jet in the class you wanted. No budget changes that.
Next, the flight length. On flights under roughly an hour, a turboprop often arrives within minutes of a jet for much less money. That is because a jet spends most of a short flight climbing and descending. On flights over about two hours, the jet’s speed saves real hours.
Then the load. Count passengers and be honest about baggage. In light aircraft, space runs out before weight does. Six people with golf bags or camera kit need a different aircraft from six people with briefcases.
In helicopters, passenger weight and air temperature matter more than most people expect, especially at altitude.
Only now does comfort come in, and it is a real factor. A cabin you can stand up in changes what a three-hour flight feels like. On a working flight, that has business value. But you choose it from what is left after the limits, not before.
One last check: ask what the quote assumes about ground time. An aircraft that waits is charged for waiting. A trip with a long stop in the middle may be cheaper with a different aircraft, or as two shorter flights, than with the obvious choice.