I agree with these splits! I would be fine with splitting it any of the above ways, though I think these would be my preference:
1) Via the main character of the (historical part of the) game. Therefore: AC 1, Ezio Trilogy, AC3, all of the rest of the games separately
2) Via the main character of modern storyline. Therefore: Desmond storyline (AC1, AC2, AC:Brotherbood, AC:Revelations, AC3), then all of the rest of the games separately*
*note: I haven't played later AC games aside from AC: Origins, so I don't even know if any of the future games share overlapping modern protagonists! My apologies if I've made a mistake anywhere.
Re: Assassin's Creed
1) Via the main character of the (historical part of the) game. Therefore: AC 1, Ezio Trilogy, AC3, all of the rest of the games separately
2) Via the main character of modern storyline. Therefore: Desmond storyline (AC1, AC2, AC:Brotherbood, AC:Revelations, AC3), then all of the rest of the games separately*
*note: I haven't played later AC games aside from AC: Origins, so I don't even know if any of the future games share overlapping modern protagonists! My apologies if I've made a mistake anywhere.