A Link to the Past is by far my favorite Zelda of all time.
When I was a kid, a friend of mine had the original Legend of Zelda and I had Zelda II: The Adventure of Link. So, I felt I had the weaker of the two games, because I preferred the top-down presentation of the original to the arcade sidescroll of the sequel. IMO, the Zelda series is perfect for a top-down style of gameplay. This isn't to say that the 3d ones aren't great too, but that's a different conversation altogether.
When I first played it, A Link to the Past was very impressive. It was exactly what I'd hoped for regarding the SNES installment of the series, because it took what I felt was great about The Legend of Zelda and made it so much better. Even today, A Link to the Past is a game I can play over and over.
I am willing to concede the fact that I've never indulged in the handheld games in the series, which is a little foolish considering my regard for the style of gameplay the handheld installments offer. So, it is difficult to say that A Link to the Past will forever be my favorite Zelda game, but it will always certainly be at the top of my list.