Charlie it really depends on a lot of factors. How fast you want the jig to sink, what is the current like, are you fishing in brush, ect ..
I have a plastic maker that uses my minnow heads on a 2 1/2" bait that he makes. I was using them on a baby shad style bait the other day and had good luck. On the same note though, a lot of guys using round ball heads were having just as good if not better luck.
Bobo