No question about it, it is the aircraft commander. That is what he/she is paid to do, and where the buck stops. That isn't to say that operations may not require a diversion to a particular airport for whatever reason. In such circumstances the commander would be expected to comply unless they had compelling reasons not to. This isn't a case of discussing whims or ego driven decisions, it is about cold hard commercial realities. Those realities would only be superceded by serious safety considerations, and it is up to the commander to decide as and when that is the case.