In my opinion Syndicate is worse.
It felt like the story and side quests were being written by multiple teams that only had a passing mention of what was supposed to happen before it. Some sequences just felt really disjointed to me. I liked the characters at first but the hammy script kind of made then unlikable trying to force conflict it didn't really do a great job building and the side quests have some god awful writing and design.
The one where Alexander Bell is distracting 2 goons so you can throw a stink knockout bomb or something was so weirdly designed from a narrative point of view. They are intimidating him you throw the bomb on his cue then they all shrug it off and silently walk like 10 paces then start harrassing him again and you do this like 3 times. It made no fucking sense.
The city is still great, but I preferred Unity. I actually liked Unity's story, main character, co-op stuff and even the side content I found fun and kinda their own thing. I couldn't wait to be done with Syndicate and I'm a bit confused how it was considered a better game/getting AC in track at the time.
Personally, worse games would be 3, Liberation(I guess, never finished it) for me with Syndicate, Revelations and Rogue battling for the next spot.