We've used Escapees Mail Service for almost 10 years now. Not once have we had a problem with their service. That cannot be said for the USPS which has lost our mail once, caused us to delay departure by several days when Priority Mail (2/3 days most locations) took two weeks (the town was not that small nor that big).
By being a member of the Escapees Organization there are many other benefits besides the mail service and we, as full-timers, have never regretted becoming members. When we went to Livingston, TX, to switch everything over, the local government officials made it a breeze as they are totally aware of the Escapees and made us more than welcome. Since then, we've handled everything by mail, phone or internet, including driver's licenses, registering a new truck, and just this past year our new Bighorn.
Everyone has a reason for their particular choice, but you cannot go wrong with Escapees. Good luck in your pursuit...