I'd say Breath of the Wild because it's so fresh and modern while still feeling like a Zelda game, I think it's amazing. Also because of the content within the game, I have played it for 135 hours (or more 'cause the Switch is weird) without the DLC.
If I would have to pick a traditional Zelda game I'd say Twilight Princess. It's the only game that kept me engaged to finish the game so there's that.