head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Competitive PvP
Large-scale modern combined-arms shooter built on destructible maps and squad teamwork.

Execution · Competitive PvP
Mechanical football control plus predicting how a human opponent attacks.
Battlefield 3 leans Execution (Competitive PvP); FIFA 16 leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 3
Gunplay, suppression management, and vehicle piloting
FIFA 16
Dribbling, defending and finishing inputs decide duels
FIFA 16 leans a little harder on reads, though the gap is small.
Battlefield 3
Human teams adapt routes and armor pushes
FIFA 16
Human opponents online adapt tactics match to match
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 3
Spawns, destruction, and vehicle drops shuffle engagements
FIFA 16
Deflections and finishing randomness swing close games
Battlefield 3 leans a little harder on optimization, though the gap is small.
Battlefield 3
Unlock paths, class synergy, and map control
FIFA 16
Formations and squad construction reward study
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.