I don't have any hard metrics on who is buying my work, some of my best clients are small-med sized businesses who are looking for artwork for office walls that is related to their industry. Others are people interested in the subject matter who find me via serach engines and referals. Many model railroaders buy my work as reference for their model building.
What I am looking for is a buyer friendly sales platform that offers streamlined purchase options for prints and stock licensing. A platform that increases sales and broadens my customer base is most desirable, that would include a keyworded site which will increase stock sales, as well as print and book sales.
I plan on filling orders myself, I prefer this for quality control. So the partners that zenfolio has is not important to me at this point.
My priorities would be snappy customer experience, multiple payment options, searchability, options for downloading digital files for stock licencing, and easy administration of the site.