One should consult these to get an accurate picture of desirability. The key reference is The Value Guide for Unipart and Multipart Porcelain Insulators . Generally, the older classic porcelain is more desirable, including glaze-welds large dry process , and insulators produced by the early manufacturers. These manufacturers include Fred M Locke, Imperial, R. Thomas and Sons, New Lexington, Pittsburg, Victor, and Ohio Brass, among others. Also, clearer early markings are more desirable than weak markings.
Rare styles are also desirable.
These multiparts date from the 1900s and had one or more of the bottom skirts curved outward. Upside down they look like lily leaves. These were fragile and not many have survived. Any early threadless insulator is quite rare and valuable. These are typically quite crude and clearly very old.