Regulators are relatively simple, but choosing the right one for you can be a complex decision.
The First Stage
Most divers only use one first stage. This makes it a single point of failure and breathing is fairly important to keeping you alive.
Go with Din
Many divers use yoke regulators and many dive operations only have yoke tanks, but there is no real reason to buy a yoke regulator. A simple, cheap adapter lets you use a din regulator with any yoke tank, but there is no such adapter that works the other way around.
Din is also a technologically superior. The oring is captured and when diving with a din reg your oring is the one sealing to the valve, not the oring that came with the tank.
Sealed vs Unsealed
Temperature Rating
Material
Most regulators are made out of plated brass as it is the cheapest. Higher-end models will have a more durable coating. Titanium is probably the second most common material followed by stainless steel. Titanium and stainless steel regs will last a lot longer. Some titanium regulators are not recommended for use with nitrox, but that is more of a problem for deco regs.
Second Stages
The second stage has a huge effect on the quality of your dive. Better ones have a lower “work of breath”. Not only is it more pleasant it’s also safer not being forced to breathe heavily because your body can eliminate the CO2 that it generates. In fact, when CO2 builds up in your body it makes your body want to breathe more. A bad regulator that is hard to breathe through will always result in higher air consumption, you won’t even get reduced air consumption for your effort.
Servicing
If you’re a simple diver with a great local shop, servicing your regulator may end up being your largest expense. Regulators don’t tend to fail completely, they just tend to slowly reduce in performance, becoming harder and harder to breathe through.
Consoles
Consoles have fallen out of fashion because modern dive computers replace all of their functions while being much more convenient.
Mouthpieces
https://a.aliexpress.com/_mOV7v5p
The versions of this mouthpiece that come from major manufacturers have a patent number, brand name and country of origin embossed right where my lips go. It is noticeable and a good reason to not pay the extra money for them.
I haven’t had success with moldable mouthpieces.