I rather dislike a bit more of the attributes in Adventure of Link over the original Legend of Zelda (the setup of the overworld, returning back to the very beginning once you die, the first Temple almost impossible to pass, etc.).
Thus I strongly prefer Zelda I. The overworld was very fun to explore--a massive labyrinth seemingly filled with a puzzle in each new section. It's enemies, while some hard to destroy, contributed strongly to the challenge, making it intriguing and enjoyable. Altogether it can be quite frustrating, but later on you feel the need to finish what you started, as in getting to a new Dungeon or even beating a Boss to get the Triforce shard there. It makes the game all the more worthwhile to play and hopefully beat.