You can use mild, medium, or hot green chiles (or a combination) and then adjust to desired heat with more jalapenos.
The flavor is very close to the original Chubby's, but not exact. Want to tweak it to get it more exact? My suggestion is to try different brands of hot sauce. Cholula's is an excellent choice, but I'm not convinced that's the brand Chubby's uses.
Commentary:
I've had more requests for this recipe than any other ... but it is top-secret and known only to the members of the Cordova family who run the original Chubby's on 38th St in Denver. So, I've tested and experimented and tested some more. You can see my first version at Chubby's Green Chili (Copycat) published a year & a half ago. I estimated it was more than a 90% match to the original, but I couldn't quite get color, texture and flavor just like Chubby's. Note: in photo above, bowl on left is the Original Chubby's while the one on the right is my copycat version. Pretty close, huh? Look at my previous version and it clearly looks different.
Many readers sent in their suggestions on how to tweak the recipe to make it just like Chubby's, and I tried all of them. Sure enough, this recipe is over 95% there. Compare the two - the addition of chili powder and hot sauce made a huge difference. I still put more meat in and I usually tone the heat down a tad (as Chubby's is very hot) - so be sure to tweak heat (chiles & hot sauce) to taste.