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

Execution · Pure Mechanics
An asymmetric horror FPS letting you play marine, alien, or predator, each with wholly different abilities.

Execution · Pure Mechanics
Keeping speed through destruction-racing chaos that punishes clean-lap plans.
Aliens versus Predator (1999) leans Execution (Pure Mechanics); FlatOut: Ultimate Carnage 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.
Aliens versus Predator (1999)
Fast aliens and panicked aim demand twitch reflexes
FlatOut: Ultimate Carnage
Holding racing lines through wrecks and ragdoll chaos tests hands
Aliens versus Predator (1999) leans a little harder on reads, though the gap is small.
Aliens versus Predator (1999)
Asymmetric multiplayer pits unlike species against each other
FlatOut: Ultimate Carnage
Rival drivers ram predictably, light multiplayer jockeying
Aliens versus Predator (1999) leans a little harder on variance, though the gap is small.
Aliens versus Predator (1999)
Motion-tracker dread and dark vents hide enemy positions
FlatOut: Ultimate Carnage
Debris and pileups scramble any planned lap
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Aliens versus Predator (1999)
Mastering each species' tools and level knowledge
FlatOut: Ultimate Carnage
Car upgrades and track shortcuts are mappable
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.