If you're adding anything to a Clouser or jig, like a spinner or some kind of tail, then the "Farrar blend Slinky fiber" is the juice to drink.
If nothing, but maybe a little flash, is added.....then use untrimmed Bucktail. The tips give it all the action it needs.
As far as swivels go.....as long as it spins freely when the fly/jig is dropping then you're good. The less weight involved in the blade system the better (I think).