I'm a bit conflicted, I like many of them from the different eras for different reasons, but most importantly, I'm not sure what I exactly think about Black Flag anymore.
While I don't particularly want the loot based system in Odyssey, the freedom in that game was absolutely fantastic and it really improved on Black Flag on that point.
Black Flag used to be my favorite with 2, but even back then I was frustrated that you didn't have a total seamless freedom, most of the islands are fake and you can't land on them, and the big ones have loading transitions to get to them, so it's not particularly immersive either.
Once you are on these islands, the freedom is also quite limited because you have different boundaries everywhere, which is fine, not all games need to be 100% open I understand it, but I really wanted more exploration in this game, being able to explore some desert islands, jungles etc, it would really fit the theme and I think it was a bit lacking on that point.
Odyssey on the other hand... 100% total freedom. You can take your boat and go to ANY island you can see, even stuff super far in the ocean. You will never have any loading, everything is seamless, you can land everywhere, you can swim underwater everywhere, you can climb anything, any moutain, there's almost no limit, it's incredibly satisfying and enjoyable, and it reminded me of what I was dreaming for Black Flag before it came out.
The only negative for exploration in Odyssey that frustrated me is that for some reason they don't allow you to explore with the little boat, sometimes you have 2 islands really close to each other but you can't travel between each with the little boat, it will sink automatically, it's useless, so you have to go to the big one which makes it more tedious, especially since I don't see a reason for this limit.
So I guess the ideal would be a sequel to Black Flag, but with the same freedom as Odyssey. Big scale pirate game with immense freedom of exploration, but with less content bloat.