Agree with Rick, I would say it all depends on the usage whether your usage is soft, semi-soft or stiff.
In my job, we use solid wires and it is the sheaths that have different properties, the use of multi-strands is for pipes and main entrances because they must be flexible.
The cost of a stranded cable is always higher than a solid cable of the same current rating because the manufacturing cost is higher and more copper is used to maintain the same load specifications.
Damn I'm drowning the fish...
In summary, what makes the difference is the quality of manufacture, example wrapped without oxygen... the properties of the sheath... and the purer the copper used, the freer it is of impurities and alloys , the more expensive it will be .