Well their stats are virtually identical...
Pinsir, on the one hand, can learn the moves Earthquake, X-Scissor, and Seismic Toss: plus it's Mold Breaker ability that can royally screw some pokemon.
Heracross, on the other hand, learns Megahorn, Night Slash, Shadow Claw, and the infamous Endure/Reversal Combo. It is, however, owned by any manner of flying type move...and susceptible to Psychic type moves which are generally more common than the rock types to which it gains neutral resistance.
I say they are perfectly equal, only suited for different sweeping roles. Were they to battle one another, the outcome would be determined solely on which one hits first (they have the same base speed, by the way). Before the 'Heracross endures and activates Salac Berry' argument comes into play, keep in mind that Pinsir can learn Quick Attack.
Thus, I vote for Pinsir to try and even things back out as they should be.