The Adventure of Link, if I had to pick one, simply because of the greater sense of a "living Hyrule" that you get (for the first time in the series, but certainly not the last)...but only by a *very* slim margin over the original Legend of Zelda.

The one balances out the other, in my opinion, and the series is all the richer for it. They're the foundation of the entire franchise, inviolate. Remove one, and the greater whole suffers.

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"Chuck Norris once visited Heaven. Needless to say, no one will be getting their 72 virgins."