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

Execution · Pure Mechanics
Party racing and arena shootouts decided mostly by platforming speed.

Execution · Pure Mechanics
Motion-controlled tennis, bowling, golf, baseball and boxing built around simple swing gestures.
Rayman Arena leans Execution (Pure Mechanics); Wii Sports leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Rayman Arena
Footrace platforming speed and arena aim decide matches
Wii Sports
Motion swing timing and accuracy decide every event
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Rayman Arena
Human rivals add light jockeying, little depth
Wii Sports
Casual local opponents add light mind games
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Rayman Arena
Minor pickup randomness in arenas
Wii Sports
Minor physics wobble and CPU behaviour randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Rayman Arena
Track knowledge gives a modest edge
Wii Sports
Simple technique tricks like bowling spin are learnable
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.