We're only going by the quality of writing (pacing, themes, logic, execution) combined with the enjoyment factor when reading it in one go, right?
Fishman Island 5/10
Punk Hazard 6.5/10
Dressrosa 7/10
Zou 9/10
Whole Cake Island 7/10 (up until the Tamatebakko explosion a 10/10, then a 3/10)
Reverie 10/10
Wano 7.5/10 (yes, it has flaws, but when you read it in one go it's enjoyable and only Udon drags quite a bit)
So FI is pretty clearly the worst postskip arc for my taste. The rest is solid, but only the short Reverie and Zou arcs really stand out imho.
Fishman Island 5/10
Punk Hazard 6.5/10
Dressrosa 7/10
Zou 9/10
Whole Cake Island 7/10 (up until the Tamatebakko explosion a 10/10, then a 3/10)
Reverie 10/10
Wano 7.5/10 (yes, it has flaws, but when you read it in one go it's enjoyable and only Udon drags quite a bit)
So FI is pretty clearly the worst postskip arc for my taste. The rest is solid, but only the short Reverie and Zou arcs really stand out imho.