If I had to choose, I would make the Shabaondy Archipelago arc into a movie. Except that I would extend the information given and powers shown of the Supernovae. Maybe get to know them better. Then all the action, make it even more dramatic and cooler looking. And of course, the movie will end with Kuma sending all the strawhats away. That would be a major twist, because then the good guys lose. Wait.. Pirates are supposed to be the bad side... Confusing.
The problem with the Shabondy Arc is that it's not self-contained. It relies on a (hilarious, but) unimportant side arc about Duval and has no real resolution even 3 arcs later. So unless you could turn Shabondy + Kuja + ID + WBwar into a movie (possible, but a lot would be cut), it would feel disappointing.
There's a reason movies and stories end with the good guys winning, so that it's not an obvious sequel cash in. I mean, imagine avatar ending where the big tree gets destroyed. You'd be confused, and then angry. Or a better example: imagine Star wars ending with Empire Strikes Back.
That is just ridiculous. Here is a topic, what arc would make a good movie, and what changes would you make to the arc to make it a better movie???
Whoever was in charge with refitting the Drum and Alabasta arcs into movies was obviously delusional. The Drum arc is too small for a good movie, the Alabasta arc too large since it was built up from the very entry of the grand line. Heck, you could argue the arc was built up from Joni mentioning the Shichibukai before Arlong Park.
The best self-contained arc that would go well as a movie, to my mind, would be the Skypeia arc. Even though it is only #5 as far as favourite arcs go in my mind, it has a beginning act, a middle act and a final act. You could easily cut out some of the cameo fights, or actually turn them into something more hectic befitting a pirate raid on an established army, and build up one villain that Worf's every single character until the main appears, effectively making the final conflict the ultimate end of the movie.
Arlong Arc was only good knowing the build up of Nami. Alabasta the build up of Vivi. W7/EL required a lot of pre-story to make it good (Ussop, Going Merry, Robin, Aokoji) and was all-in-all way too large. TB was too short and as mentioned before, the SA+KI+ID+WBwar arc is either too long, or too uncontained.
Another possibility could be the entire East Blue Arc. Sure, a ton of shit would get cut out, but then again a lot of the East Blue arc was pointless time wasting nonsense to give Oda enough people in each arc to face off against all the Strawhats (Don Kreig's "Pearl" anyone?)
those crazy bastards.
