Amazed by the amount of people who thinks that the best series are those consisting of 2-3 games. I mean, Halo? Come on, that's 1 game, re-released with shinier armors a few times. I did enjoy the first game, but that's that.
Has to side with the masses on this one though, would have to put Mario or Zelda up on the pedestal as the most awesome series of all time. Were it about publisher/developer though, I would say Blizzard, hands down.