Putting in time with all 3, going to have to go with Horizon. The bow mechanics, story, and world all meshed together so well and really struck a chord with me.
The Witcher 3 comes in a really close second, and I feel that the story in H:ZD gives it the edge. Not that the Witcher 3 had a bad story, it was great and I was really interested, but it was pretty formulaic and nothing really wowed me.
There were things I liked better about W3 and things I liked more in H:ZD, but as a whole H:ZD gets my vote.
It's hard to rate Breath of the Wild in there. While there are a lot of similarities with the open world, it feels really different in overall gameplay. It is an amazing game, and for pure exploration and wonder Zelda beats the other 2 hands down. A lot open world games get the same critique that the world feels empty. With the huge world that Zelda presents, it does not have this problem. The world is so alive and there are so many things to see and find that you can literally wonder around aimlessly for hours upon hours finding new things and not get bored. Where I don't feel like I could say that about the other 2. Their worlds look great, but I wouldn't explore for the sake of exploring.
Even though Zelda knocks the exploring out of the park and I love the art style, I don't find it as fun to play as the other 2.
At the end of the day, all 3 are fantastic games and you can't go wrong picking any one of them up to play. If a poll gets added I see Witcher 3 taking this pretty easily. It's just been out for a lot longer and is multiplatform.
