I've had good luck with UShip
UShip has been featured on Storage Wars, the cable TV show, and thus has had a lot of exposure the last few years. I started using them in 2009 or so, a few times per year. I have used them now 12-15 times or so. Having experience with them, they are my preference at this point. I have also used UCrate. UCrate is great because you get very reliable, standard trucking company LTL shipping services and expert packing is available, but they can be pricey. Sometimes its worth it when a highly desired machine is being shipped.
With UShip you may be using a little hauler guy and his Chevy Silverado that he also uses to drop his kids at school to move your freight, or a major trucking company. The shipper always has the choice to accept or decline a carrier's offer so we are in control at all times.
In the old days UShip was an auction based service, where providers would reverse bid on a shipment to drive down the price. That is still an option, but UShip apparently prefers shippers (us) to name their price and let carriers agree or pass. My recent experience (twice) is that they say my named price is very unlikely to attract bids, but in each case carriers took them with no problems. Most of my experiences have been good or nearly flawless. Their website is largely self-explanatory, but I can offer advice to anyone - just e-mail me.
Gordon