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

Execution · Competitive PvP
Late-90s arcade football execution with couch-versus prediction and bouncy luck.

Execution · Competitive PvP
Stick-skill football execution with opponent prediction in versus play.
FIFA 99 leans Execution (Competitive PvP); UEFA Euro 2008 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 99
Quick passing and shot timing in arcade-leaning football
UEFA Euro 2008
Pass timing, dribbling and finishing decide matches
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA 99
Couch opponents can be conditioned and baited
UEFA Euro 2008
Versus humans, baiting tackles and disguising attacks matters
FIFA 99 leans a little harder on variance, though the gap is small.
FIFA 99
Era physics produce regular fluke goals
UEFA Euro 2008
Bounces and deflections add football's usual noise
UEFA Euro 2008 leans a little harder on optimization, though the gap is small.
FIFA 99
Simple formations and known exploit angles map fast
UEFA Euro 2008
Formations and squad selection sit underneath
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.