I think Wimbledon was the best, because of the best final (5 setters between 2 of the big3, number 1 and 2 seeds, almost 100 winners from Federer, end at the 5th set tie break, drama etc...) and also other quality matches (Nadal/Kyrgios, Djokovic/Hurkacz, Goffin/Medvedev, Nadal/Federer).
Then I would say Roland Garros, because of great matches all tournament long (Mahut/Cecchinato, Hoang/Verdasco, Tsitsipas/Wawrinka, Federer/Wawrinka, Djokovic/Thiem, Nadal/Thiem)
Then the US Open just thanks to its final. And in last position the AO with only Tsitsipas/Federer to remember (and zoning Djokovic in the final)