I would have to say that it is definitely the goalie (in hockey and soccer). Like has already been mentioned, a team wins and loses games based upon how hot their goalie is. If a goalie is in a slump, regardless of how well the rest of the team is playing, they will not win many, if any games. On the other hand, if a goalie is hot...like Halak was for the Habs last year in the playoffs, and even an average team can go far. The Habs didn't win it all last year...BUT, they definitely went a lot further than they should/would have had it not been for Halak.
The QB in football, though important, isn't as important, and can be overcome in ways that the goalie can not. For example, in Super Bowl XL, despite the fact that Ben Roethlisberger had one of the worst games at QB in Super Bowl history (22.6 QB rating...BY FAR the worst of any winning QB), the Steelers still managed to win the game 21-10. Their running game and defense (plus a 42 yard TD pass from a receiver) made up for a lousy game by Ben.
I'll take a solid netminder over any other solid position player in any other sport. I believe he is just that important.:2 cents: