I am interested to read Sandeep's reply and read any articles he links to, but I will give you my opinion now.

The SOLID185 is the linear element and the SOLID 186 is the quadratic element. Since you have a well structured mesh, you will have more detail in the results with the SOLID186 quadratic element because it can represent curvature in the stress results along its edge, even when the edge is a straight section. Better yet, since you have some cylindrical surfaces in your bodies (holes and shafts), the SOLID186 element can represent the geometric curvature of the geometry, while SOLID185 has straight edges so the edge of a hole will show facets with SOLID185 and you will need a finer mesh than if you use SOLID186 which can have curved edges.

Both elements support Rate Independent Plasticity, which includes Multilinear Isotropic Hardening.