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

Execution · Competitive PvP
Out-executing and out-predicting another human in frame-precise duels.

Execution · Grand Arena
Frame-perfect execution fused with constant prediction of an adapting human opponent.
Super Street Fighter IV: 3D Edition leans Execution (Competitive PvP); Ultra Street Fighter IV leans Execution (Grand Arena).
Ultra Street Fighter IV leans a little harder on execution, though the gap is small.
Super Street Fighter IV: 3D Edition
Links, anti-airs and motion inputs gate every level of play
Ultra Street Fighter IV
One-frame links and FADC timing set a brutal hands ceiling
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Super Street Fighter IV: 3D Edition
Footsies and conditioning a human opponent decide matches
Ultra Street Fighter IV
Footsies and conditioning the human opponent is the core duel
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Super Street Fighter IV: 3D Edition
Almost fully deterministic once inputs land
Ultra Street Fighter IV
Almost nothing hidden once both characters are known
Ultra Street Fighter IV leans a little harder on optimization, though the gap is small.
Super Street Fighter IV: 3D Edition
Frame data, matchup knowledge and punish routes underpin everything
Ultra Street Fighter IV
Frame data, matchups and option-selects form deep studied theory
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.