First off, the stock reg on any kingman product has never impressed my at all. In my opinion, it not even much of a reg. Ever taken one apart? Very primitive at best.
The second question I would ask. Is what do you plan on running in the near future? If your going to use CO2, make sure that the regulator you buy, can handle CO2. Some of them cannot and will cause it malfunction.
If your going to use Nitro. A regulator such as a Vigilante is the best buy. They run about $50. You can purchase them preset for high pressure. Which if you plan on placing this on a spyder or any kind of blowback marker, you need a high pressure high flow reg.
Another question that I want you to ask your self. What is your budget like? Would you better off sticking with a cheap expansion chamber/front grip and using the money for a nicer barrel?
I have seen some of these guys with $100 regs on a $100 marker. See a problem with that?
If you want to read reviews about regs and expansion chambers go to:
Hope this helps.