.../
.../And one last thing, "the best you can afford" isn't necessarily the most expensive, especially when it comes to regulators. A $150 HOG works just as well as the $700 Titanium Aqualung which works just as well as the Scubapro. These days any reg you buy with a reputable name (and most with a "no-name") on it will last a lifetime if serviced properly and will breath nearly identically under water.
I agree with this to a point.
It's true that most respected companies make quality regulators and that those high end regulators all breath pretty well.
However:
1. Companies differ quite a bit in their ability and willingness to support older regulators. Aqualung and Scubapro are two companies that still support most of the regulators they've every made, at least in terms of annual service kits. For example is you bring in a Mk 1 with an R109 Adjustable second stage, or a MK III with a R108 High Performance second stage, I can still get the annual service parts to service it, and they'll even still be in stock.
These are regulators that are over 45 years old, but they can still be serviced and even better, in some cases they can be upgraded. For example you can take an R109 "Adjustable" and give it balanced poppet system from the "Balanced Adjustable, and that poppet will be the same poppet used in the current S600. Scubapro in most cases designs improvements so they are backward compatible into older models, giving them the equivalent of a service life extension program.
The only Scubapro regulators that I'll have trouble getting annual service parts for are the Mk VII (for the honker side of the reg, the other side is a plain old Mk V), the Pilot, the Air 1, and the first generation Air 2.
The machined "hard" parts are a little more difficult to come by as companies eventually run out of parts stocks, but parts like regulator first stage bodies and pistons don't generally wear out, unless the regulator literally has tens of thousands of dives or, more commonly, has been badly neglected and allowed to corrode.
The same applies with Aqualung/US Divers regulators. Pretty much all the various Conshelf series reg can be serviced as can their numerous descendants.
At the other extreme you have companies that sell variations on a few OEM designs and they don't always have the same staying power in terms of long term parts and service support, and while you'll see similar designs with different brand labels, they are not always equal when it comes to internal tolerances and quality.
Hog is a good example. Their initial offerings were priced very well and SOME of them breathed very well. Others were however dogs due to how the wide tolerances in parts sometimes stacked. And I've heard from a few divers and techs who saw some failures such as burst diaphragms that just should not have ever happened.
My impression is that they've since got their quality issues under control and the tolerances seem to be more consistent, but I still hesitate to recommend them.
Dive Rite is a good example of a company that sells great regs, but comes up a little short on long term support. They sell very high quality regulators, and while the design is a common OEM design, they make some of the components in house and they order the rest of the parts to very high specifications. They are high quality regulators with very good performance, and over the years they keep getting better.
But that's also their weakness. You run a real risk of buying a Dive Rite reg today that won't be fully supported just a few years from now as they make evolutionary changes, but those changes are not made with an eye toward backward compatibility. Dive Rite is owned and operated by very active divers and they continually make things better, but they don't always consider the long term impact on customers who have the older stuff, and it's a flaw in the business model that costs them some sales.
I recently needed a pair of right hand inlet regulators and bought a pair of XT2 second stages. They perform every bit as well as my Scubapro G250 and G250Vs, and they are less than half the price of a new G260 - but I have no illusions about getting 25 plus years of service out of them. Unless DR changes it's business model slightly, they won't be supported to the same degree that a G260 would be. I also got the XT2s at cost, so the paid price to MSRP ratio is about 1 to 4, which is hard to beat in the short term and if I am left hanging 5 years from now rather than 20 years from now, it's still a break even deal on a cost per year basis.