head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Practiced Mastery
Ezio's Renaissance revenge tale of parkour, assassination, and villa-building across Italy.

Optimization · Practiced Mastery
Twin assassins seize Victorian London borough by borough with gang warfare and a rope launcher.
Assassin's Creed II leans Optimization (Practiced Mastery); Assassin's Creed Syndicate leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed II
Counter-heavy combat stays forgiving
Assassin's Creed Syndicate
Rope-launcher traversal and simple brawling
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed II
Guards follow scripts
Assassin's Creed Syndicate
Gangs are scripted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed II
Fixed world and missions
Assassin's Creed Syndicate
Fixed activities
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed II
Villa economy and route planning, lightly
Assassin's Creed Syndicate
Gang upgrades and borough takeover planning
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.