Killzone or Horizon, which is the better series and why

[Shadow1980]

I've only played Killzone 2 & 4, but I prefer Horizon by a wide margin. Even though they still have a lot of the same problems other open-world games have (e.g., repetitive copy-and-paste checklist objectives, too much time spent just on traversal), they bring enough to the table to more than make up for it. The combat, especially against the machines, is fun, the art style is great, the world/setting is amazing, and I love the story and characters.