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
High-speed tag-team execution and human prediction in gleeful early-Versus chaos.

Execution · Competitive PvP
A platform fighter where reading opponents and precise execution both drive victory.
Marvel vs. Capcom: Clash of Super Heroes leans Execution (Competitive PvP); Super Smash Bros. for Nintendo 3DS 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.
Marvel vs. Capcom: Clash of Super Heroes
Chain combos, assists and infinites demand fast precise hands
Super Smash Bros. for Nintendo 3DS
precise inputs and combo execution required
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Marvel vs. Capcom: Clash of Super Heroes
Baiting a human's assist call or super is the duel
Super Smash Bros. for Nintendo 3DS
reading opponent habits and mixups
Super Smash Bros. for Nintendo 3DS leans a little harder on variance, though the gap is small.
Marvel vs. Capcom: Clash of Super Heroes
Hidden characters aside, everything is public
Super Smash Bros. for Nintendo 3DS
item spawns add randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Marvel vs. Capcom: Clash of Super Heroes
Team composition and infinite-combo knowledge define the meta
Super Smash Bros. for Nintendo 3DS
matchup knowledge and combos solvable
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.
full breakdown
Marvel vs. Capcom: Clash of Super Heroes →
full breakdown
Super Smash Bros. for Nintendo 3DS →