1. Jaya-Skypiea
2. CP9 (Long Ring - W7 - Sea Train - EL - post-EL)
3. Baroque Works
4. Summit War (Sabaody - AL - Impel Down - Marineford - post-war)
5. East Blue
Jury's basically still out on the New World stuff not just because I've found the quality to be lower than before (which I do), but also because it's getting harder and harder to neatly categorize the story into arcs. They're so much more interconnected than before, every island has contained important setup for future ones and the story flows pretty seamlessly rather than being split up into self-contained story arcs.
Fishman Island was pretty good, but can't measure up the big 'uns all on its own. The "Doflamingo arc" (Punk Hazard - Dressrosa), despite being a huge disappointment in many ways, is stronger than the "Big Mom 1 arc" (Zou - Totland) for me. It had proper setup and build-up which led into kind of satisfying conclusions and closure on all the major story beats.
Even though I actually think the latest two arcs we've had are better, looking at their individual quality, they don't feel "done" yet in the same way. Zou was setup for Wano and beyond as much as it was set up for Totland and WCI left more threads hanging, intentionally eschewed closure than any other arc. That's not bad writing or anything like that, it's definitely deliberate, but it also means I can't really judge them the same way I would other arcs/sagas. My current gut feeling is that the time of neatly contained arcs is completely over by now and it's going to be one long seamless stretch from here to the end. By then we'll have one gigantic arc that contains everything from Zou to round 1 with Big Mom, to Wano/Kaido, to Elbaf/round 2 with Big Mom, and beyond.
As far as strictly individual arcs/islands are concerned:
1. Skypiea
2. Water 7 (incl. Sea Train)
3. Arabasta
4. Enies Lobby (incl. post-EL)
5. Jaya
6. Marineford
7. Impel Down
8. Drum Island (the MOST underrated arc!)
9. Zou
10. Baratie
Gets tough by the end. Whole Cake Island, Sabaody and Arlong Park all kinda duke it out for that last spot along with Baratie, it could really go either way. Zou remains the best post-timeskip arc in my books, it was short but executed to near perfection.
Chopper
