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

Execution · Competitive PvP
Arena fighting built on baiting substitutions and timing punishes against humans.

Execution · Competitive PvP
Tests grapple timing and predicting an opponent's next move choice.
Naruto Shippuden: Ultimate Ninja Storm 3 leans Execution (Competitive PvP); WWF SmackDown! leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Naruto Shippuden: Ultimate Ninja Storm 3
Substitution timing and combo confirms need decent hands
WWF SmackDown!
Grapple timing and reversal inputs decide exchanges
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Naruto Shippuden: Ultimate Ninja Storm 3
PvP revolves around baiting substitutions from human opponents
WWF SmackDown!
Against a friend, predicting grapple choices is the game
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Naruto Shippuden: Ultimate Ninja Storm 3
Support meter and item randomness barely matter
WWF SmackDown!
Some reversal and AI randomness in season mode
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Naruto Shippuden: Ultimate Ninja Storm 3
Team composition and awakening knowledge add a thin layer
WWF SmackDown!
Move-set knowledge and stamina management are shallow but real
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.