I have used all of them.
I can't say any is better than the others. ER Shaw is cheapest, but you have to wait the longest. I used a lot of Shilen because I could have one in 3 days from Brownells.
One barrel company that i have extreamly good luck with is the cheapest barrel on the market I know of Adams and Bennet from Midway USA. I used about 15 of them a few years ago. The least accurate one I used was a 30-06 re-barrel for a friend's son. It "only" would shoot 3/4" groups at 100! yds. Not bad for a 69 dollar barrel.
Another one I did for the same man was a 270 Winchester and it shot 5 rounds under 1/2", and did so for 3 different shooters in the same morning.

If your inletting is right, and your barrel and chamber work right too, you'll find they all shoot sub-MOA.
For a 300, I would recommend at lease a 24" and a 25 or 26 is probably better if you want full velocity.
Are you going to do the work yourself? If you are not, tell your gunsmith you want the chamber set to only .0015" headspace. I do this will all belted mags except for 416s and 458s. Those i give .003"
Good luck and good hunting.
Steve