head to head
Quake Live asks more than Halo 3, and the gap is execution.

Execution · Pure Mechanics
Trilogy capstone whose equal-start arena multiplayer defined a console generation.

Execution · Pure Mechanics
Browser-era refinement of Quake III, the benchmark for raw arena FPS skill.
Halo 3 leans Execution (Pure Mechanics); Quake Live leans Execution (Pure Mechanics).
Quake Live leans clearly harder on execution.
Halo 3
Precision aim and grenade-melee timing
Quake Live
Rail aim and strafe-jump movement are the purest hand test
Quake Live leans clearly harder on reads.
Halo 3
Equal-start fights reward predicting humans
Quake Live
Duels are mind games against an adapting human opponent
Halo 3 leans a little harder on variance, though the gap is small.
Halo 3
Equipment pickups and spawn variation
Quake Live
Symmetric arenas, full information, almost no randomness
Quake Live leans a little harder on optimization, though the gap is small.
Halo 3
Power-weapon timers and map control
Quake Live
Item timing and map control are deeply solvable
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.