I'm modeling a system which requires effective mixing theories in two places. First, I'm modeling a shell of proteins around gold nanoparticles as a homogenous mixed material of protein (n=1.5 or so) and water (n=1.433).  Secondly, the nanoparticles are forming a monolayer, so I am modeling that layer as a dielectric slab of gold mixed with water.  

I've seen many different mixing theories like Brugemann, Maxwell-Garnett and others, and am never really clear when certain ones are more accurate than others.  For my situation, which would you recommend?  What about when coverage is low, medium and higher in terms of the number of inclusion in the media?

Thanks