Sebastian wrote:
But neither originality nor beauty of tone can be measured
Anything can be measured in a way that's more useful that if you didn't measure it at all.
Key word: "useful". If it serves your purpose, you can use it.
If you prefer to disregard all that you say that can't be measured "objectively" to come up with a "definitive answer", then that's your choice (and a very practical one), but I'm sure you know that by selectively considering or ignoring factors to come up with a "definitive answer" you inevitable end with a subjective assessment, more like an opinion (a.k.a. "a Treasure Moment Fact").
I guess the "definive answer" bit depends on the Question asked.
If the question is "Which president generated more jobs in my country?" the answer is very straightforward. Just check the statistics (which were recorded by someone else, years ago) and answer right away.
If the question is "Who was the BEST president in my country?", I'm guessing you won't get too much consensus there.
In the end, people will agree and disagree with you.
It's all about opinion. If I were and object, I'd be objective, but I'm a subject (a person).