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 · Twitch Chaos
Co-op zombie shooter whose AI Director reshuffles every run to keep teams honest.

Execution · Twitch Chaos
Kart racing with random item pickups and drift timing on themed tracks.
Left 4 Dead leans Execution (Twitch Chaos); Madagascar Kartz leans Execution (Twitch Chaos).
Left 4 Dead leans a little harder on execution, though the gap is small.
Left 4 Dead
Headshots, melee shoves, and special-infected reaction time
Madagascar Kartz
Steering, drifting and item timing matter in races
Left 4 Dead leans a little harder on reads, though the gap is small.
Left 4 Dead
Versus mode adds human ambush mindgames
Madagascar Kartz
Rubber-band AI is scripted, not adaptive prediction
Left 4 Dead leans a little harder on variance, though the gap is small.
Left 4 Dead
AI Director randomizes hordes, items, and specials
Madagascar Kartz
Random item pickups swing race outcomes
Left 4 Dead leans a little harder on optimization, though the gap is small.
Left 4 Dead
Team spacing, route choice, and resource discipline
Madagascar Kartz
Track shortcuts and item management reward knowledge
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.