I don't think it really matters. There are people who have had problems with UPS and only use Fedex or the Post Office. There are people who have had issues with either Fedex or the Post Office and will never use them again.
Of course, there are people who never had a problem with any of them.
I would just use whichever is easiest for you, if you are near a post office send it express overnight, if near a ups store bring it in and let them tell you which costs less.