I've seen both Pacman and Pitfall being claimed as the best-selling Atari 2600 game so I'm skeptical about this. Is Pacman actually the most-distributed only? Cause Pacman was packed-in with the system at one point or something.
Pitfall may have been the biggest-selling third-party game, but I doubt it was the outright #1 seller for the system. I don't see nearly as many of them around as Pac-Man.