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
Arcade racing with Mario Kart-style power-ups bolted onto licensed cars.

Execution · Twitch Chaos
Item-luck kart racing with a creation suite bolted on.
Blur leans Execution (Pure Mechanics); LittleBigPlanet Karting leans Execution (Twitch Chaos).
Blur leans a little harder on execution, though the gap is small.
Blur
Racing lines and dodging shots demand car control
LittleBigPlanet Karting
Drifting and weapon timing decide most races
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Blur
Human racers bait and time power-ups against you
LittleBigPlanet Karting
Human racers add light prediction in item battles
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Blur
Power-up pickups and incoming attacks add chaos
LittleBigPlanet Karting
Random item pickups swing positions constantly
Blur leans a little harder on optimization, though the gap is small.
Blur
Track knowledge and pickup routes are learnable
LittleBigPlanet Karting
Track lines and shortcut knowledge give a modest edge
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.