head to head
Neither is simply harder - they are hard in different places. Baldur's Gate II: Shadows of Amn demands more variance; Fallout: New Vegas demands more execution.

Optimization · Pure Optimization
The deepest optimization puzzle in the Infinity Engine lineage, rewarding encyclopedic knowledge of 2nd Edition AD&D systems.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Baldur's Gate II: Shadows of Amn leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Baldur's Gate II: Shadows of Amn
Pause-and-plan removes twitch entirely; micro-placement has marginal value
Fallout: New Vegas
Shooter inputs with VATS assist
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Baldur's Gate II: Shadows of Amn
Enemies run scripted behaviour patterns, never modelling your tactics
Fallout: New Vegas
Scripted factions and enemies
Baldur's Gate II: Shadows of Amn leans clearly harder on variance.
Baldur's Gate II: Shadows of Amn
Loot randomization and enemy ability use create hidden-information layers
Fallout: New Vegas
Some loot and crit RNG
Baldur's Gate II: Shadows of Amn leans clearly harder on optimization.
Baldur's Gate II: Shadows of Amn
Mage spell sequences, dual-class builds and Spellhold routing define mastery
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
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.