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
Crude comedy 3D platformer of boss fights, parodies, and set-piece variety.

Execution · Practiced Mastery
Aim and movement through a fully scripted campaign that route knowledge solves.
Conker's Bad Fur Day leans Execution (Practiced Mastery); Half-Life: Source 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.
Conker's Bad Fur Day
Varied platforming and shooting set pieces
Half-Life: Source
Aim, movement and platforming through Black Mesa's gauntlets
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Conker's Bad Fur Day
Bosses and enemies fully scripted
Half-Life: Source
Marines and aliens run impressive but fixed scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Conker's Bad Fur Day
Linear, authored content throughout
Half-Life: Source
Fully authored campaign, nothing random
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Conker's Bad Fur Day
Context-sensitive solutions are learnable
Half-Life: Source
Route knowledge and resource management trivialise replays
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.