What is a good IPv4 block size to sell?

Potential Sellers of IPv4 resources often ask questions such
as:

• What is the most common size of IPv4 block sold?
• Should I sell a /20 or a /19? Which will sell faster?

At IPswiTch Networks Ltd, we experience demand for block sizes that mirror the overall market.  John Sweeting, ARIN’s Senior Director for Registration Services, presented the chart shown in Figure One at the ARIN 43 meeting (April 2019).