I've had problems with all of them, but fedex has had the least problems.
UPS I can guarentee whenever my regular driver has a day off, my stuff WILL get damaged or delivered to the wrong place.
USPS they either come damaged, or never get here, or the carrier is too lazy to climb the stairs to the front door and they just slip one of those "sorry we missed you" notes in the box on the road ( very annoying when you are home all day waiting on a package and STILL have to go to the post office to get it. The terminal manager at the local post office knows my voice over the phone if that tells you haw many problems I've had with them )
I won't ship via USPS and have stuff shipped USPS reluctantly if it's the only option.
A couple of years ago I was browsing through the USPS website and was noticing where they were bragging about their delivery statistics and how they handled X amount of packages a day with onlt X percentage lost.
Well a little quick math told me that USPS looses enough packages every day to fill an airplane hanger.
----------Robert