head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Pure Mechanics
Motion-controlled racing where fighting the Kinect is half the physical test.

Execution · Pure Mechanics
Holding clean lines at speed through traffic on memorisable point-to-point roads.
Sonic Free Riders leans Execution (Pure Mechanics); The Need for Speed leans Execution (Pure Mechanics).
The Need for Speed leans a little harder on execution, though the gap is small.
Sonic Free Riders
Full-body Kinect steering is a physical (if unreliable) motor test
The Need for Speed
Holding racing lines at speed through traffic is the test
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Sonic Free Riders
Human races add slight item-timing prediction
The Need for Speed
AI rivals and police follow fixed behaviour
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Sonic Free Riders
Item pickups inject kart-style randomness
The Need for Speed
Traffic patterns add mild run-to-run noise
The Need for Speed leans a little harder on optimization, though the gap is small.
Sonic Free Riders
Track shortcuts are shallow knowledge
The Need for Speed
Track knowledge and car choice settle quickly
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.