Fil Tec is the leader in prewound bobbins. Superior has pre wounds which are very good to match their threads. I was told to always take the paper backing off the prewound bobbins, not many know to do that if they want. The pre wounds are wound with perfect tension and has much more thread on them then any machine winding can do. I buy my prewounds here:
http://www.bobbincentral.com/