Rubber bushings are designed for the "street" use only vehicle. They provide a more factory like ride. These bushings do not need to be lubricated, but will not provide you with that "tight" suspension feel.
Polyurethane bushings are designed for a performance like ride. Polyurethane may squeak if not properly lubricated. You should use a lubricant that will not wash away. Once the lubricant is washed out or contaminated from road grime the lubricant will no longer be effective. You will need to re-lubricate.