I haven't seen much of Syndicate actually. Probably because my brother is too busy making me freak out over the new Star Wars: Battlefront, that's coming out soon.
I've seen a lot of people say that 3 was their least favourite, which bugs the hell out of me, cuz i enjoyed it. (Not as much as Black Flag and Rogue, but more than all the Ezio ones.) Lol, must just be me, cuz my brother didn't like it much if memory serves. The book version of 3 is SO MUCH BETTER than the other books though. Ironic really. Worst game according to many, but the best book according to me and others.
Haytham is the most awesome dude in any game ever, except maybe Thane and Garrus from Mass Effect. Connor is......alright. My brother hates him though. And i didn't like the ending much, that was the worst bit of 3. Not cool, Connor, not cool.
Loads of people like Ezio the most. I find him frequently topping polls as the best character. My favourite Assassin would be Altair, probably followed by Edward, but Haytham is still the best.