Chrome-moly or stainless for barrel?
Application 3gun. Length 18", 223 Wylde chamber, 1:7.7 twist, hbar profile.
To get back on to the discussion.
I used to compete extensively in 3-gun using Colt HBar chrome barrels. The barrels did not hold me back. If the barrel will keep the groups to 1 moa, you have all that you really need for 3-gun. Probably the most challenging target you would expect to see is steel plates (8-10 inches) at about 300 yards. With a barrel / bullet combination that can do 1 moa, then it remains your skill at position shooting that will solve the shooting problem.
My chrome Colt HBar barrels all shot 1 moa with good ammo. I would expect that almost any custom barrel that you are looking at, and assembled by a competent gunsmith will shoot 1 moa. So for Chrome vs Stainless - if you only need 1 moa, I do not think Chrome vs Stainless will really make a difference that you will notice.
My most recent barrel is Stainless but I could have gone either way, it was more a question of what was available.
Regarding the HBar profile. At the time I was seriously and actively competing, compensators on rifles were not truly effective. So an uncompensated HBar had an advantage over a lightweight uncompensated barrel. Today some of the new compensators are absolutely awesome at muzzle control, so I no longer feel that a HBar is an advantage. My new barrel is a midweight profile and with my compensator the muzzle movement is insignificant. BUT transitioning from one target to the next is noticeably faster with the midweight vs the HBar.
We need to get together so you can try a Colt Hbar upper vs the Stainless mid weight (I can spin the same type of compensator on both for a fair comparison). I think you will see that the midweight is faster to move from target to target.
Assuming that you going to be shooting in "Open" or "tactical limited" then a 18" should be good. If you were looking at shooting "limited" then sight radius is king and get the longest practical barrel you can.