While the op manga has dropped in quality quite much (fishman island), became repetetive(dressrosa) and progressing at a low speed (dressrosa, wci 🤦♂️), for me it is the best.
Why? Because I grow up with one piece and the moments I had with it, were great. Better than with any other manga (and yes, I read QUITE A LOT) + judging based on the whole series, it is still the best.
Imo.