"Always goes bang!" is an impossibility since the gun must be reloaded periodically and all mechanical things have problems on occasion. A more correct requirement is that the mean round count between failures be sufficiently large that the odds are low that I will not have to use my skills to get the gun back into action, draw a second gun or engage the Sneaker Defense System.
I don't rank my requirements because there are many of them, all of which are important. Obviously, concealment, weight, height, length, capacity and sight radius are important. But, attributes such as: recoil pattern with defensive ammo, smooth/easy on the hands, sufficient mag well bevel, ability to do maintenance without a gunsmith, aftermarket parts availability, installing sights, cost of magazines (do you hear me SIG and HK?), custom grip availability, existing gear and reloading setup, lack of ammo sensitivity, and location of controls are all very important to me.
I look at the whole gun rather than review just a few items. Sometimes, I won't know that a gun is unsuited for carry until I take a class with it and fire many rounds through it on the range. The SIG P220 SAO is a perfect example. It is the SIG I always wanted. Unfortunately, the thumb safety is misplaced for my hand and is not adequate for my shooting style.