We can rank these characters according to two categories, "low" and "high" in the social hierarchy. Beyond this simple distinction, we can draw some finer rankings, but these will be limited. (There is not enough evidence distinguishing the characters beyond broad categories to generate a complete top-to-bottom ranking.)
First, we can easily identify the characters that fit into the "low" and the "high" social categories.
- Low: Candy, Crooks, Curley's wife and Lenny.
- High: Slim, George, and Curley.
Two of these characters can be argued to occupy a middle ground, socially positioned between the categories of "low" and "high". These characters are Candy and Curley.
Of the characters filling the bottom of the social order, Candy is closest to being like the men above him. He is white and he is mentally competent. However, Candy is physically incapable of doing heavy work. This relegates him to the lower group, which is why he is included in the scene with Crooks, Lennie, and Curley's wife in the stables.
Curley technically belongs to the higher group because of his financial standing. His many character flaws lead to a general disrepect for his person, but Curley carries some power none-the-less. Curley's quickness to fight and his embarassing marital situation do not completely erase his underlying potency.
His position in society has encouraged this behavior; his real strength lies not in his fighting ability but in his power to fire any worker.
Also, we can look at Curley's wife and Crooks as occupying the lowest echelon of the social order, with Crooks being told at one point that Curley's wife has power over him because of his skin color. Curley's wife then would occupy the rung above the bottom rung on the social ladder, with Crooks occupying the last rung.
This is only one interpretation however. We might also argue that Crooks occupies a higher position because the men on the ranch respect him in ways that they do not respect Curley's wife or Lennie. In this view, Curley's wife and Lennie share the lowest social positions.