head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Twitch dodging and shooting layered over memorised arcade stage routes.

Execution · Practiced Mastery
Score-attack remix of Pac-Man built around herding huge ghost trains at high speed.
Metal Slug leans Execution (Practiced Mastery); Pac-Man Championship Edition DX leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug
Dodging dense bullet patterns and precise shots carry every credit
Pac-Man Championship Edition DX
Blistering speed demands frame-tight cornering
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug
Enemies follow fixed arcade scripts, never adapt
Pac-Man Championship Edition DX
Sleeping ghosts follow deterministic trains
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug
Spawns are nearly deterministic once a stage is learned
Pac-Man Championship Edition DX
Board layouts are fixed and learnable
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug
One-credit clears come from memorising routes and spawn patterns
Pac-Man Championship Edition DX
Routing ghost trains for maximum score chains
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.