Just did my FET for the quarter, and by dollar amounts the significantly best selling size is 1/8, followed in order by 1/4, 1/32, 1/16. Due to the high cost of lead free metals I only get a few custom requests for heavier heads so can't say what that demand is like for cheaper lead heads.
So, if you're serious about selling jig heads and want to start with a production mold the RHB-8-48 allows you to pour 4 each of the most popular tapered barb collar round head 1/8 and 1/4 oz. sizes per pour set. An additional RHB-8-1632 will cover the 1/16 and 1/32 sizes.
This is just for starters. If you continue as a bizness you will keep adding molds per customer requests. I'm up to at least 70, and I know some of our members have more.