All the above post have merit.
The only one that was not mentioned was the Cadillac of regulators. The Poseidon brand.
Any brand that you choose will ultimately depend on the tech. servicing them.
I'll take a stab at Poseidon, which I have used almost exclusively for decades, for both recreational and professional use. I have had the opportunity of trying out most every brand and have still found no real reason to switch; and they have now made their service kits available, over the counter -- and any manufacturer that is still unwilling to do so, would never be on my shopping list.
I currently have one of my 2004 MK3 workhorses disassembled, along with a Cykon 300 from the 1970s, both ready for the ultrasonic cleaner.
The XStream, mentioned earlier in this thread, and now over twenty years old, is bar none, the finest first stage I have ever owned; simple to service with a near-permanent diaphragm, which never required any costly or spoogy environmental sealing, even under the ice, and can be paired with any of Poseidon's second stages, dating from the Cyklon, which has barely changed, save for some minor material updates, since 1958, through to the Jetstream (now at over forty years old!); and the XStream, which is nearly the same in terms of its construction, though the second stage valve was just reduced in size.
Concerns raised about "soaring IPs" are largely mythical and can be attributed to any brand through poor or no maintenance. Mine are all rock-solid; and my only experience over a ridiculous number of dives, with a regulator that ever "blew" was an untested rig from a shop that I grabbed at the very last minute to make a boat; and the OPV, then located on an Odin ("Jetstream") LP hose, eventually did its job, and I was able to breathe normally during a controlled ascent -- and didn't even bother to use the pony bottle . . .
