I'm going on my personal experience here and I've had or have most of the barrels mentioned here but by and large Les Baer is going to be hard to beat.
My Rainier Ultramatch 18" intermediate is sub MOA for match ammo and MOA for NATO type ammo at 100 yds. I like the company. They stand behind their claims. It's easy for me to hit 600 yard 10" targets with 77gr match ammo. I haven't tried further yet.