I'd say either A Link to the Past or Ocarina of Time, since they're laying the foundations of much of the series's lore, as well as much of the core gameplay mechanics for 2D and 3D respectively. The very first game obviously also layed down some of the basics, but that one's extremely difficult and would feel obsolete for a modern newcomer. I suppose something could be said about playing Skyward Sword first as well, since that one's the first chronologically.
I'd suggest first-timers should stay away from any of the direct sequels in the series like Majora's Mask or Link's Awakening until after one played the 'primary games', even though they're absolutely brilliant, I think they'd be a confusing start. Not that you'd have a bad time obviously though.







