In a metagame sense, the DM has the power. It's been my experience that DMs are always in greater demand than players, and it's always easier for a DM to find a new player than for a player to find a new DM. Especially an individual player vs. the DM, because that player is going to have to convince the other players to go through the trouble of searching out a new DM, rather than just dumping the player and continuing to play until a replacement player is found.
In a campaign, the players and DM hold equal power. While the DM controls all the other action in the campaign world, the players still control their own characters, and the game centers around those characters. A player can just as easily demolish a campaign as a DM can, which is why the best games are composed of people who recognize that all parties--players and DM--are working toward the same goal, for everyone to have fun.