They are all GOAT players and each and everyone of them can beat the other on most surfaces, bar maybe Clay if Nadal is in full form.
Their head to heads are quite even despite many variables and factors that are into account, and most matches they played were very tight and could go either way bad a point or two, or a choke or two.
So whatever someone says or whoever favorite they have you have to admit that.
For example Djokovic leads Federer 3:1 on grass, yet in two of those matches particularly 2019, it could have easily went the other way.
On other surfaces where they all played more matches its even more obvious where it could have been 7:7 or 10:4 or 4:10..depending on a few points here or there.
Peak for peak in their best years which would be 2005-06 for Fed, 2011-12 for Djokovic and 2008 or 2013 for Nadal
In slams:
Australian Open:
Djokovic has an edge against Federer and Nadal
Federer has an edge against Nadal
French Open:
Nadal has a huge edge against Federer and Djokovic
Federer and Djokovic are about even, small differences mean the difference between the victor
Wimbledon:
Federer has an edge against Djokovic and Nadal
Djokovic has an edge against Nadal
USO:
By far the hardest to judge, I would say they are all equal here, despite Djokovic's lack of titles he has shown some impressive performances, they all have, so I think it would come down to very little things amongst them all
when 2 players are technically and game-wise equally good then it is precisely the head that decides and that is precisely why nole has the upper hand over fed. it is no coincidence that he saved 6 MP in 3 slam matches that he won against fed. their h2h is 27-23 for nole. if fed had won those matches it would have been 24-26 for fed. their slams matches are 11-6 nole, would be 8-9 fed. slam finals are 4-1 nole, would be 2-2. but it is not luck but the head that made it go over in nole's favor. because the more important the match, the more important the set, the more important the game in the match and the more important point in the game the more it goes to nole's advantage.
all matches: 27 (+ WO) - 23 for nole
matches before final: 14 - 17 for fed
finals: 13 (+ WO) - 6 for nole
matches outside GS: 16 - 17 for fed
GS matches: 11 - 6 for nole
GS matches before F: 7 - 5 nole
GS finals: 4 - 1 nole
WTF matches: 3 (+ WO) - 3
WTF matches before F: 1 - 3 for fed
WTF F: 2 (+ WO) - 0 nole
fed is better in TB during the career for 0.5% units than nole. but:
their h2h TBs: 16 - 12 for nole
Non-critical TBs: 12 - 12
deciding TBs: 4 - 0 for nole
fed has taken more sets than nole in their h2h, 73 - 74 for fed but:
non-critical sets: 59 - 69 for fed
deciding sets: 14 - 5 for nole.
and then we have the 3 slams matches with 40-15 at MP.