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
Open-world racer where banking risky speedpoints against human cops drives the tension.

Execution · Twitch Chaos
Tests drift execution and track knowledge under item-roll chaos.
Need for Speed: Rivals leans Execution (Pure Mechanics); Sonic & Sega All-Stars Racing leans Execution (Twitch Chaos).
Need for Speed: Rivals leans a little harder on execution, though the gap is small.
Need for Speed: Rivals
Open-road control with pursuit tech timing
Sonic & Sega All-Stars Racing
Drift chaining and boost timing decide clean laps
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Need for Speed: Rivals
AllDrive mixes human cops and racers in
Sonic & Sega All-Stars Racing
Item duels versus humans add light prediction only
Sonic & Sega All-Stars Racing leans a little harder on variance, though the gap is small.
Need for Speed: Rivals
Dynamic open-world encounters and weather
Sonic & Sega All-Stars Racing
Item rolls and All-Star moves shuffle placements
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Need for Speed: Rivals
Risk-versus-bank speedpoint economy
Sonic & Sega All-Stars Racing
Track shortcuts and character choice reward learning
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.