Best: Assassins Creed III - I felt the beginning was very surprising, with a bunch of great locations and crazy timeline jumping. I'm not impatient, so the intro wasn't an issue for me. That game had amazing snow landscapes (my favorite scenario) with a ton of things to do. It was also the only AC which constantly introduced new items, features and places throughout the whole game, until the end basically. Not to mention it featured naval battles before AC IV, hunting, setting up traps, rocks and trees which you could actually climb and much more. The Assassins sequels after III felt inferior because so many gameplay features were removed. Thankfully it sold very well, but ultimately only a minority seemed to enjoy AC3.
Assassins Creed IV Black Flag
Assassins Creed Syndicate
Assassins Creed Unity
Assassins Creed Bloodlines
Assassins Creed II
Assassins Creed
Worst: Assassins Creed Liberation