I've used all three above and they are equally durable IMHO. But, you do need an oven or other heating source big enough to accept the barrel or the barreled action.
I'm sure there are barrel butchers out there who will do it for you, at a price, and some who will go to a more durable black by giving the parts a copper wash and then blacking the copper. Or, a similar plating process? You gets what you pay for.
Absolutely the best one is "Black T" by Walter E Birdsong. He died a while back, but his sons still run the business and the process hasn't changed. You won't find a better coating. Cerrakote is OK.
Use your own resources, type in "Walter E. Birdsong" You will find a bunch of search results.... The one that takes you to his site is the right one. They are the only ones that do it. How do you think I found it... search engines work!
Cerakote is a LOT tougher than Black T. I have had both done, there is no comparison. The Black T looks nice but it is not as durable. If you are trying to do it on the cheap, the Brownells stuff is decent but not much tougher than regular spray paint. I have a buddy that uses a special stove paint and heats it on with a heat gun. He builds real expensive BPCRs. Anything you use other than bluing, will require some grit blasting to prep the steel should you want stuff to stick.
The Melonite treatment is probably toughest of all but I had a barrel that wouldn't shoot after the treatment so be aware of that possibility. If you have a CM action and bolt, you can probably have them treated that way. I had mine done and it looks good and is harder than a file. Just wish the barrel hadn't turned out the way it did.
I have a couple stainless actions that i would like to have black. Not real sure the best way to do this. These are benchrest actions so i dont want anything that will add tolerance issues. melonite may be the way to go, but some folks think melonite process is to much heat for gun related items? I wouldn't know. I talked with a fella the other day that does a DLC process but he wouldn't give me a written guarantee on the work so unless i find someone respectable that has had this done, i will pass. Not sure what route to take. Lee
I have used KG guncote and have been satisfied with the results. The application requires blasting, application and baking. If Im applying to CM steel I apply zinc phosphate before the KG, I skip the ZP for stainless steel. The product runs about 60 bucks for a qt. it goes a long way