What is the story, the graphics, etc. Please explain.
AC Black Flag.
It takes place in different islands in the Caribbean and in my opinion it is the best AC. The story is just great, you also meet well-known pirates like Blackbeard, there are treasure hunts, battles against master ships, etc. But it is still a "classic" AC in terms of the combat system.
The newer the better the graphics, very simple, but it is rather muddy on the 360 anyway.
My favorite is Assassins creed 2. Everyone with Ezio, brotherhood and revelations too
Black flag
if you like pirates, fight with ships and the best AC part there's no alternative.
I would start with part 1 then simply after series games. I also played everyone on the 360. Without spoiling now
If you want to understand the background story, you should proceed chronologically, i.e. H. Start at Part 1 and end at Odyssey. Valhalla isn't out yet.
Each part has its own special charms, whereby I didn't like Origin and Odyssey because they are too RPG-heavy.