head to head
Neither is simply harder - they are hard in different places. Ultra Street Fighter IV demands more execution; Warcraft III: Reign of Chaos demands more variance.

Execution · Grand Arena
Frame-perfect execution fused with constant prediction of an adapting human opponent.

Optimization · Grand Arena
Blizzard's hero-centric RTS where build-order theory meets surgical unit micro against humans.
Ultra Street Fighter IV leans Execution (Grand Arena); Warcraft III: Reign of Chaos leans Optimization (Grand Arena).
Ultra Street Fighter IV leans clearly harder on execution.
Ultra Street Fighter IV
One-frame links and FADC timing set a brutal hands ceiling
Warcraft III: Reign of Chaos
Micro of heroes and units decides fights
Ultra Street Fighter IV leans a little harder on reads, though the gap is small.
Ultra Street Fighter IV
Footsies and conditioning the human opponent is the core duel
Warcraft III: Reign of Chaos
Scouting and out-guessing a human opponent's tech
Warcraft III: Reign of Chaos leans clearly harder on variance.
Ultra Street Fighter IV
Almost nothing hidden once both characters are known
Warcraft III: Reign of Chaos
Creep routes and item drops add randomness
Warcraft III: Reign of Chaos leans clearly harder on optimization.
Ultra Street Fighter IV
Frame data, matchups and option-selects form deep studied theory
Warcraft III: Reign of Chaos
Build orders, creeping routes, and matchup theory run deep
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.