The most telling statement was from Jack Kramer, great player in his own right, mastermind of the professional tour in the 1950s/1960s and probably the most influential man in tennis history.
Kramer grew up idolising Don Budge, and called him the GOAT. He kept this opinion for many, many decades (through the rise and fall of Gonzales, Rosewall, Laver, Borg and Sampras, to mention only the greatest who he saw).
Yet, a few years before his death, he changed his mind from Budge to Federer.
No man's opinion is foolproof, yet if there is one man I would trust to rank the GOAT above all others, it would be Jack Kramer.
And guess what? In the end, he picked Federer.