I agree with the Proof Research barrel recommendation, when I buy prefit AR 10 Barrels, they have been the most consistent. I use a variety of bolt carrier groups, they all work, none has ever failed. So I have a majority of Toolcraft bolt carrier groups, with the .062" firing pin. Never used any high dollar bolt carriers, as I found it unnecessary to pay extra. They are identical, with one of two basic metals in the body and the exact same on the bolt....many made by the same company, just add a cool logo and charge extra bucks. The steel and heat treatment specs are all within parameters. So some slouch didn't stake the carrier key bolts well ...no big deal restake them...rounded corners...I highly recommend Proof barrels for LF ARs. They come with the gas tube so you know you have a matches tube. Proof has the gas length figured out on their barrels. Pair it with a JP bolt. If you don't want to buy their entire BCG. I have built two LF ARs and they were and have been drama free. Gas tuned within 10rds. I think the key to success has been builders kits for matched receivers. Matching of Proof barrels and JP bolts. JP SCS for adjustability in the buffer tube lengths and buffer weight adjustability. I've used SLR Sentry 7s for both builds. Lantac EBCGs are also really nice. I'm using the EBCG with a substituted JP bolt in the 6.5CM in a Proof barrel.
I used to be a big proponent of McGowen barrels but their quality of work on their blanks has slipped massively. I've received wrong orders and many folks here have gotten some pretty shitty chambers and muzzle threads. I recently thought their blanks were still at least good and ordered a .224 blank. Gunsmith just chambered it. When I picked it up I asked him what he thought of it. He cringed and said uncomfortably like he didn't want to tell me that the OD of the contour was not concentric to the bore. So when he indicated off the bore and then started spinning the barrel it was helicoptering all over the place. Haven't shot it yet.
If you don't want to go Proof, I'd suggest Rainier Ultra Match barrels. I would really encourage you not to skimp on the BCG and barrel. At least not the barrel. Consider a custom from CLE or Craddock.
So I'd put your money in the Proof SS barrel, no carbon fiber for me..today.. none other, for a general cartridge build, for a good start hopefully their quality will continue...I've had quite a few from well known makers having less quality or stopped the lapping procedure to soon, when borescopeed. Its also putting the parts together, squaring, checking, gluing drilling, turning, milling may be required. Just bolting it together, ...is just that. Is it sq or perpendicular, fit?
I ordered a McGowen barrel for a specific project because of the twist available. We will see. Not concerned about a small amount of runout between the barrel and bore...there is always a small amount somewhere. As mine are both just blanks, and will be chambered, threaded, OD turned, one blank will likely be AR 10 and require the full treatment, of gas block journal, gas port, barrel extension, threaded & chambered, plus thread for the brake...accuracy starts with the barrel, bedding, then bullet it likes. Then there are a bunch of tweaks and procedures that may help...sometimes alot. Centering the bolt carrier, and squaring the reciever, are examples.