Plastic (or possibly a completely dead urethane) should be used for most spare combinations. There are sometimes exceptions such as double wood, but otherwise, the choice of plastic for spares should be automatic. As far as weight, stay with what you use on your primary ball to keep mechanics as consistent as possible.
When it comes to plastic, brand really doesn't matter. I've used Spare Storms, Target Zones and White Dots, and they all do the job.
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