We have used ShipRush for two years and done several thousand shipments. They help us when we call, and we have shipment lookup on the web site. It is really great that we can get a new computer and we didn't even need to move the shiprush data file, because the shiprush web site has all our shipments.
We can tell you to for sure try shiprush. It is free to test it out. We used the free fedex version for a long time and did postal shipping in dazzle, but then we found we could do our postal in shiprush also, and that works great. They do not charge for multiple stores, which is good since we have three web stores.