Leghorns aren't a bad breed. The entire class of birds is a bit flighty. Leghorns, like Minorcas and Anconas are bred to forage on their own, lay eggs and stay fit and trim. Like the Hamberg's in the continental class, these birds can be a bit more high strung, depending less on humans and more on their wits. Now the production-type leghorns are often easily handled. In short, they are not mean,just scare easily - probably in the shy category. I'll take my chances with leghorns way before I trust an Ancona or Minorca to be gentile.
Standard fighting games are mean, but not the old english bantam variety. Modern games tend to be docile. Cochins and silkies as well as wyandottes have no choice. I think they are more or less lazy. d'anvers can be classified in both friendliest and hostile. My hens are sweetheart. A coule of the roosters bounce off my leg everytime I enter the barn.
Polish... well, their polish. They have the ability if handled to be quite docile