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
Futuristic large-scale Battlefield where teams besiege flying Titan carriers.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
Battlefield 2142 leans Execution (Competitive PvP); Tom Clancy's Rainbow Six: Vegas 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 2142
Gunplay, piloting, and Titan boarding need solid mechanics
Tom Clancy's Rainbow Six: Vegas
Aim and snap-to-cover gunplay punish slow hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 2142
64-player human teams shift fronts and Titan assaults
Tom Clancy's Rainbow Six: Vegas
Multiplayer angles and pushes demand reading human opponents
Battlefield 2142 leans a little harder on variance, though the gap is small.
Battlefield 2142
Large maps hide flanks; battle chaos obscures information
Tom Clancy's Rainbow Six: Vegas
Terrorist hunt spawns vary modestly between runs
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 2142
Unlock paths, squad roles, and Titan strategy reward planning
Tom Clancy's Rainbow Six: Vegas
Room-entry planning and map knowledge are studyable
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.