At the moment, with business slow, UShip provides an excellent way of choosing a shipper. I shipped a sailboat from Buffalo New York to Eugene Oregon. The fact that I was able to extend the posting allowed for several shippers to combine my shipment with other business.
I think this may be the key to receiving the best possible bid and would advise starting the process far enough ahead, and with enough flexibility to allow for shippers to give you ample consideration.
UShip's reminders, their handling of the process and the ultimate result were, for me, excellent.