Unless you are planning to shoot more than 5,000 rounds thur you barrel it is a mute question.
CM steel is durable , Stainless is stronger. Nickel content determines strength. An example would be 18/8 chromeium/nickel steel is a standard. Carbon content effects temp resistance, the quence process effects hardness and durablity. Its all a conpromise. Just get a barrel that you like and is pleasing to your eyes. Rifle gas systems will give your barrel more life than carbine gas systems.