Little to add, apart maybe from said website having
rules for cropping in order to have some sort of consistency in the way screeners judge photos. These may or may not coincide with one's personal taste, but on that site playing goes by the rules.
Of your Sukhoi example, DJ, I like the 3rd one best and the 2nd one least. Indeed, I like the original more than the first crop in this case. The first crop to me is not really an aircraft filling the frame nor is it an airfield scene with the Sukhoi, like the original. If aiming for a centred fuselage, I would probably cut off part of the right wingtip (outside the chute).
My answer to your question is like that of most others: I do not crop in some general way per photo, or it must be 'the way I mostly like the result'... But even that can vary, for instance based on intended use.
Erik