Solid copper or stranded copper for speaker cables? What is your choice and why?

I had old copper speaker cable made by Audioquest (don't know the model).  The cable contains only two solid copper wires, one is thicker than the other. As I recalled, Audioquest claimed back then that thicker wire primarily carries lower frequency signal and the thinner wire is responsible for the rest.  I actually have not seen this type of design nowadays, BUT when listening and comparing it with the stranded wire (either 12 or 10 gauge) cable, I found the dynamic range is greater, and the bass is tighter and has more weight.  What do you think?