I was torn between ALttP's Dark World or OaA's Past.
I do love how much the world changes between OoA's Past and Present. It feels like a new world, but is familiar enough to still be navigable and to have many moments of wonder as you see things that no longer exist but people tell stories about, or things that are just forming that you know well in the Present. It was a great way to use time travel, I think, and it makes the game really interesting.
But I had to go with ALttP's Dark World. ALttP was my first video game, and I thought Agahnim was the final boss. Beating him after so much effort only to be dragged into another world, one filled with more mysteries, more danger, and a lot more adventure was mind-blowing. The Dark World always felt like a scary, dangerous place where I didn't belong and it really hammered home to me that I had to stop whatever ruled this place from reaching Hyrule. Anything seemed possible in the Dark World. Trees talk or shoot bombs. Some people are weird creatures, like a ball, or a hand, or a little devil thing. There were so many dungeons and so many secrets. It was incredible.