Atomics are over engineered, and not in a good way. They have some neat features but they add complexity that is not really desireable in a regulator. They do of course have the appeal that goes with anything that is badly overpriced.
In terms of going the distance I have two thoughts:
The Scubapro Mk 5 has been around since the Mid 1960's is one of the most cloned regs ever made and offers a wonderful combination of performance, features and bullet proof reliability. The same can be said for the Mk 10.
Similarly, the Scubapro R109 Adjustable (and the later R156 Balanced Adjustable) is a solid design that has also been going strong for 40 years and if updated to BA standards and with the current s-wing poppet, breathes every bit as good as the current S600.
So...if it comes down to one singel hose reg for the rest of my life with limited parts availability, I'd take either a Mk 5 R109 or Mk 10 R156.
The same is true for the PRAM Nemrod mentions. The basic DA Aquamaster design is well made, well designed, requires little service and is very durable and relaible. When you add the Phoenix nozzle to it and get the resulting Phoenix Royal Aquamaster (PRAM), you get the same relaibility with updated Titan/Conshelf first stage parts, even better performance and the capability to support and octo, power inflator, dry suit inflator and SPG.
In 49 more years, when the DA Aquamaster design turns 100, I suspect it will be the only 100 year old reg that is still being used on a regular basis.