Which of the 3 scullcaps is best for medicinal use
It depends on which medicinal properties you are after.
Scutellaria lateriflora is a relaxing nervine so to cool and soothe the nervous systems for headaches, irritability, insomnia, etc.
Scutellaria baicalensis is more bitter thus is a relaxing nervine plus affects the liver so is used for insomnia and headaches like the above but also have a liver stimulating effect as well so used for liver fevers and liver heat.
Scutellaria barbata is again a relaxing nervine but is also an anti-inflammatory. So it is used for similar nervous system issues but also for inflammatory conditions such as cancer, migraines and other inflammatory diseases.