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

Execution · Pure Mechanics
Tests NES-hard execution and rote memorisation of brutal fixed stages.

Execution · Pure Mechanics
Comic-panel beat 'em up notorious for punishing health drain and tough fights.
Battletoads / Double Dragon leans Execution (Pure Mechanics); Comix Zone leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Battletoads / Double Dragon
Unforgiving brawls and vehicle stages punish any input slip
Comix Zone
Brutal one-life brawling demands clean play
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Battletoads / Double Dragon
Enemies run fixed NES-era scripts
Comix Zone
Enemies follow fixed attack scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Battletoads / Double Dragon
Everything is deterministic once stages are memorised
Comix Zone
Everything is placed and scripted
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Battletoads / Double Dragon
Memorising stage layouts and enemy spawns is mandatory progress
Comix Zone
Panel routes and item use are memorizable
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.