Easily the original The Legend of Zelda. Even with all the Randomizers and ROM Hacks out there, which I do try as well, I still do a complete playthrough of the original frequently. Last year, I attempted (and completed) a "No Sword Run" for the first time. I especially love the freedom of how you begin your quest. Even though it has no value until paired with the Magic Wand, I always go into Level 8 way earlier than I'm supposed to (or need to) and get the Magic Book just because I can.