Pac-Man is very basic and has the same maze for all the levels. The ghosts also follow a set pattern which means if you can memorise the patterns, it is easy to get a high score. Also the fruit bonus always appear in the same place.
Ms PacMan has four different mazes. Ms Pacman moves around the maze faster than Pacman. The ghosts do not follow patterns making the game much harder. Fruit bonuses pop out of the warp tunnels and bounce around the maze. Ms Pacman has a lipstick and a bow.
Ms Pacman is considered to be one of the best classic arcade games ever and competition for high scores is still popular. Back in the day, if you didnt have a high score on this game, you were nobody in the world of arcade high scores.
PacMan started it all but Ms Pacman is a far more refined game experience. If you get the choice between owning these games, always get Ms Pacman. Amongst collectors, it is very common and popular meaning you dont have to pay too much to get an original cabinet.