head to head
Neither is simply harder - they are hard in different places. Spy vs Spy demands more reads; Worms 3D demands more execution.

Reads · Pure Mind Games
A split-screen trap duel testing prediction of where your human rival hid the bombs.

Execution · Competitive PvP
Artillery touch, human prediction and weapon economy in destructible 3D terrain.
Spy vs Spy leans Reads (Pure Mind Games); Worms 3D leans Execution (Competitive PvP).
Worms 3D leans clearly harder on execution.
Spy vs Spy
Simple movement and item fiddling under time pressure
Worms 3D
Judging grenade arcs and wind in 3D takes real touch
Spy vs Spy leans clearly harder on reads.
Spy vs Spy
Guessing where the rival spy laid traps is the core duel
Worms 3D
Predicting where a human hides and strikes next matters
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Spy vs Spy
Item locations are hidden information each round
Worms 3D
Wind, crate drops and terrain chaos swing turns
Worms 3D leans a little harder on optimization, though the gap is small.
Spy vs Spy
Trap-and-counter knowledge forms a learnable layer
Worms 3D
Weapon economy and positioning math reward planning
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.