1. Assassin's Creed Origins - Beautifully constructed open world that's almost entirely accessible by horse, camel, or foot. The gameplay and progression are the smoothest in the series, and it has minimal naval combat. Origins is the Assassin's Creed I have the least amount of complaints about after investing 100 hours into the base game + DLC.
2. Assassin's Creed Odyssey - Has many of the same pros as Origins, and is improved in several big ways (side quests for sure), but it's definitely a lot more grindy, combat has extremely jarring difficulty spikes (especially when enemies use fire weapons), and the game forces the Adrestia on me more than I ever cared to mess around with. I would describe it as a well-baked Origins with a few unsavory ingredients.
3. Assassin's Creed Unity - Love this game too death; Arno is my favorite protagonist in the series, and between the Murder Mysteries and Helix Rifts, Unity is probably my favorite in terms of side content (AC3 is close). The open world is super detailed with seamless interior transitions, and the best designed city for parkour. I also loved the co-op and Dead Kings DLC. A game like Unity designed around the CPUs and SSDs of the next gen consoles would be spectacular.
4. Assassin's Creed Syndicate - Definitely my least favorite of the bunch, but it's not a bad game by any means. My biggest problems with it are how the repetitious gang warfare stuff is so heavily integrated with the open world, the punchy combat system, and the dour visuals compared to Unity.