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-sized motion-timing contests with learnable per-event techniques.

Execution · Pure Mechanics
Island-themed collection of twelve motion-controlled sports showcasing the Wii MotionPlus accessory.
Mario & Sonic at the Olympic Winter Games leans Execution (Pure Mechanics); Wii Sports Resort 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.
Mario & Sonic at the Olympic Winter Games
Motion-timing and button precision decide every event
Wii Sports Resort
MotionPlus precision in swordplay, archery and bowling
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mario & Sonic at the Olympic Winter Games
Local human rivals add mild prediction in head-to-head events
Wii Sports Resort
Local versus duels involve mild feinting
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mario & Sonic at the Olympic Winter Games
Events are fixed; minor physics wobble
Wii Sports Resort
Slight physics and CPU pattern randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mario & Sonic at the Olympic Winter Games
Each event has a learnable optimal technique
Wii Sports Resort
Each event has small learnable technique optima
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.