Link's Awakening, or Oracle of Ages and Oracle of Seasons.
If you do Ages/Seasons, you need to do them together to get all the benefits of the password system they used in the games. I'd suggest playing through Seasons first and then using the end game code to play through Ages.
ALLTP. Work your way up from the 2-D to 3-D games. Follow the release order.
Does that mean when he gets to OoT (again) he has to play Majora's Mask and Twilight Princess simultaniously because apparently MM is a paralell universe, while TP takes place between OoT and WW, so then he'd need WW on the side.... *brain implodes due to weird-ass timelines*
Cloud and Sephiroth - battling each other since '97 for your amusement Give it a rest already!
Anyone who's played that many should have played The Legend of Zelda already, but I don't suppose Link's Awakening or Minish Cap are bad choices either.
The only two Zelda games I managed to NOT play are the first two, actually.
I suggest the Oracles or Minish Cap. Those are the only Zelda games that I've beaten countless times. Every other, I've beaten like, twice or three times at most (except for SS. I'm working on the Hero Mode of that one)
The DS games aren't that great. Whenever you see those, you should just keep walking.