head to head
The Jackbox Party Pack 3 asks more than Garry's Mod, and the gap is reads.

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

Reads · Bluff & Deduction
The pack with Trivia Murder Party and Fakin' It, built on out-guessing the room.
Garry's Mod leans Reads (Light / Casual); The Jackbox Party Pack 3 leans Reads (Bluff & Deduction).
Garry's Mod leans a little harder on execution, though the gap is small.
Garry's Mod
Varies by mode; base sandbox is undemanding
The Jackbox Party Pack 3
Phones-as-controllers, near-zero dexterity.
The Jackbox Party Pack 3 leans clearly harder on reads.
Garry's Mod
Social deduction modes like TTT involve humans
The Jackbox Party Pack 3
Trivia Murder Party and Fakin' It reward reading the room.
The Jackbox Party Pack 3 leans a little harder on variance, though the gap is small.
Garry's Mod
Hidden roles and player chaos in popular modes
The Jackbox Party Pack 3
Random prompts and question draws.
Garry's Mod leans a little harder on optimization, though the gap is small.
Garry's Mod
Contraption building rewards systems knowledge
The Jackbox Party Pack 3
Light trivia and betting math.
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.