head to head
Neither is simply harder - they are hard in different places. Garry's Mod demands more execution; Quiplash demands more reads.

Reads · Light / Casual
Source-engine sandbox whose community modes range from building to social deduction.

Reads · Bluff & Deduction
Party game where players write joke answers and the room votes for the funniest.
Garry's Mod leans Reads (Light / Casual); Quiplash leans Reads (Bluff & Deduction).
Garry's Mod leans clearly harder on execution.
Garry's Mod
Varies by mode; base sandbox is undemanding
Quiplash
Typing a joke has no dexterity test
Quiplash leans clearly harder on reads.
Garry's Mod
Social deduction modes like TTT involve humans
Quiplash
Winning means modeling this room's shifting comedic taste
Quiplash leans a little harder on variance, though the gap is small.
Garry's Mod
Hidden roles and player chaos in popular modes
Quiplash
Prompt draws and matchups are luck
Garry's Mod leans a little harder on optimization, though the gap is small.
Garry's Mod
Contraption building rewards systems knowledge
Quiplash
Some joke formats reliably score, but rooms adapt
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.