I think the world of BOTW has the best topography of any open world game, as it is crafted for the free climbing and the paraglider, but the game has way too many moments of frustration (breaking weapon, limited stamina, climbing in the rain) compared to the convenient gameplay of Horizon in which I was absorbed in like in no other open world. Horizon is not only the most beautiful open world ever created, it is driven by a charismatic character and by an appealing narrative that want you to understand the origins of this world. On the other hand it's "funny" to think all those fantastic cutscenes from the BOTW story trailer with Zelda were actually memories from the past, eh.
In Horizon, roaming randomly for the first time in the western part of the map to face the new beasts and discover the new biomes (canyon, jungle, desert) without really looking a the map will let me the best memories in terms of pure exploration. In the end, while beautiful at times and very rich as a whole, BOTW world is too big for what it is, and the Ubisoft formula is in fact more present in Zelda since there are twice the towers to climb than there are long necks in Horizon (and those are arguably the most creative way to do towers).
Note that I got the platinum in Horizon while I've still lot of things to see in BOTW, but I doubt my opinion will change much as the mechanics and the philosophy of this Zelda are now very clear to me.