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
Arcade positioning and pop-order planning against deterministic bouncing balloons.

Execution · Practiced Mastery
Momentum-driven execution over fixed levels rewarding memorised routes.
Buster Bros. leans Execution (Practiced Mastery); Sonic the Hedgehog 3 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.
Buster Bros.
Dodging splitting balloons while firing demands precise positioning
Sonic the Hedgehog 3
Holding speed through fixed hazards demands sharp reactions
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Buster Bros.
Balloons bounce on pure deterministic physics
Sonic the Hedgehog 3
Badniks and bosses repeat identical scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Buster Bros.
Weapon drops vary slightly per clear
Sonic the Hedgehog 3
Levels never change between runs
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Buster Bros.
Optimal pop order per fixed stage layout is learnable
Sonic the Hedgehog 3
Route choice and emerald collection reward memorised play
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.