For me, it's BotW.
It's a great game, but I don't personally think it's a great Zelda game.
The things that make a Zelda game a Zelda game are very similar to the things that make a Metroid game a Metroid game -- the core gameplay loop that over the course of the game you get new abilities/items and those allow you to reach new places and get things you couldn't get before. Full disclosure I've only played about 9 hours of BotW because after that I lost interest, but as far as I can tell that core gameplay loop is what they removed from the game that makes it feel so different from all the others. Dungeons aside, weapon durability aside (though I love dungeons and hate durability), them giving you all your tools right off the bat and the only real "progress" being figuring out new ways to use the tools you already have just didn't do it for me.
Skyward Sword is my favorite 3D Zelda game, precisely because I think it does dungeons and puzzles and items so well and I don't mind smaller, dense areas as opposed to a wide open, empty field, so I'm sure my opinion will be immediately discarded. lol