I personally like UPS. To me, they are more accurate in the info given to you. You can monitor your shipment, and know exactly when it arrives, and who signs when accepting your package. I have my package arrive day before we arrive and I have my confirmation w/person who signed with me. Have never needed it and never had a problem using UPS to ship down to WDW and have done several times.
I've not used fedex for shipping to WDW, but for shipments to my home from suppliers, I've had to call fedex several times to figure out what comments mean in their tracking info.