I remember A Link to the Past being absurdly easy -- like, I beat it in a day or maybe two when I bought it as a kid. I know there are lots of secrets to go explore on the side, and I realize that a fair bit of what made the two NES Zeldas hard was grindiness, but I dunno, it was recognizably easier even before I had any kind of a chip on my shoulder about such things. I don't remember feeling any particular satisfaction in beating it, while the original Zelda felt like a huge victory. That said, this is me trying to remember feelings I had a quarter century ago (30 years for the original), so maybe if I went back and replayed them both it would be less obvious now.
I also remember thinking that the plot elements actually weakened A Link to the Past -- the plot was thin but there was just enough of it to feel kind of railroady and lame at the start, and too melodramatic or something. Again, this is how I felt as a chipper 11 year old, not some jaded old man. I mean, Zelda had snippets of dialogue, but there wasn't any pretense at giving a narrative for what you were doing (outside the goofy manual), and that made it feel even more open and exploratory.
So I'd go with the original, not just because it was groundbreaking but because I remember finding it more satisfying than any of the follow-ons.