I designed and made a mold for use with various plastic baits, as I got tired of them slipping down, even with a wire or lead barb.
I rarely use the Ultra Minnow jigs, other than for tying them with hair, and agree with Fishermanbt, they're better with a wire keeper added, as that helps hold a plastic on even when tied with hair.
I've also modified a Sparky head mold, and added a barb. I like that head style as it sits on the bottom without falling over, but otherwise, I would go with a Bullet Head mold, in the saltwater versions, if holding a plastic is the primary use. The Bullet head protects a plastic pretty well, and tends to go through grasses very well if you are fishing anywhere that has some grasses. It also bounces off of shell pretty good too.
This is my jig, the white one. I only pour them in 3/8 & 1/2 ounce and primarily use them for freshwater bass, but they also work well for inshore saltwater. The next photo is a bullet head I use. It's actually from a Hilts mod, but Do It had a similar mold. Since this photo was taken, I've added a wire keeper to this jig too, so it's got both the lead barb & a wire keeper so hold plastics very well.