I ship 100's of packages a week and use almost entirely USPS. Compared to the other guys they are the best price on most things and are far more reliable. They are also far better at honoring insurance claims.
The Hope Diamond was shipped via registered mail to the Smithsonian museum. It's for security and a paper trail, not speed. I ship a a handfull of registered packages a week and they are slow, but I've never ever had an issue with them, even to some sketchy third world countries that are notorious for "lost" mail. (read light ******** postal workers)