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

Execution · Competitive PvP
Stick-skill football against human opponents whose habits must be read.

Execution · Competitive PvP
Basketball shot-timing and scheme-reading against human or scripted defenses.
FIFA Soccer 13 leans Execution (Competitive PvP); NBA 2K13 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.
FIFA Soccer 13
Ball control and finishing inputs decide moments
NBA 2K13
Stick handles and shot release timing decide possessions
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA Soccer 13
Online humans keep adjusting their patterns
NBA 2K13
Online play is constant scheme and tendency reading
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA Soccer 13
First-touch randomness and deflections add chaos
NBA 2K13
Shot RNG and loose-ball physics add noise
NBA 2K13 leans a little harder on optimization, though the gap is small.
FIFA Soccer 13
Tactics and squad setup are a studied layer
NBA 2K13
Playcalling, rosters and matchup exploits 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.