Most AR15 barrels (indeed rifle barrels in general) are either 4140 or 4150 Chromoly Steel, either with a chromium lining in the bore and chamber or not, unless they are 416 or 410 Stainless Steel.
So you see your question is a bit unanswerable as anyone that doesn't have a SS barrel basically has a Chromoly Steel barrel, whether chrome lined or not.
Did you mean to say chrome-lined?
I have both lined and unlined.
I recommend the chrome-lined bore and chamber because of the corrosion resistance and ease of cleaning. There is a reason why modern military weapons all have a chrome-lined bore and chamber.
Well worth the $40 or so price difference.
_DR