It was toss up for me between Film Gold and Film Z. But in the end, Film Gold won out for me. I know everyone tends to dislike Film Gold for whatever reason but the heist/gambling atmosphere of the film was so unique for One Piece and the fact that most of the Strawhats got their own (albeit quick) individual fights places it leagues ahead of Stampede and Z for me.
Z felt like it was all over the place with random island hopping while Gold’s fixed location helped the story to develop in a realistic and concise manner. Although the antagonist of Z might have been a “cooler” character than Gran Tesoro, Gran Tesoro’s backstory is leagues and bounds more compelling than the likes of Z and Bullet.
If you like cool flashy fights you’re going to like Z and Stampede. If you prefer story driven narratives, you’ll probably prefer Gold more.