Some people are confused about which regulator to choose for their HPA setup.
The two most popular are the Empire and Storm Regulator. The Empire has an on/off switch which means you can in theory store your tank on the regulator itself and not have to remove the tank (which you should anyway). That means if there’s any small air leak in the system, you can just store it switched off so the air doesn’t leak. Kind of like a battery.
The Empire also has a pressure gauge that starts at 0, so it’s easier to physically see what PSI you’re using, but from a performance standpoint, it doesn’t make a difference. It just means if someone asks you what PSI, you can tell them.