As I mentioned in another thread; Federer is the most artistic, Nadal the most athletic, Djokovic the most intelligent.
As for GOATs debates in any field, I find them more of a media thing or mererly a reflection of human passion for ranking, than being rigourous logic or science
1) You can't...
I see it this way: Federer is the most artistic, Nadal is the most athletic, Djoker is the most intelligent.
If you're fit enough, thus putting fitness aside, then the mind would give you a heck of an advantage; and I'm a Federer fan.