Factory or Aftermarket Action ?
I've used several different actions for approximately 2 dozen custom builds,
All with Benchmark Barrels and one Bartlein
Weatherby Mark V, Rem 700, Husqvarna HVA small ring Mauser, Kimber Montana, Defiance Rebel, Win 70 CRF, Stiller Predator, Carl Gustaf
I'm not sure from an Accuracy standpoint once they have been Trued&Squared any action is more accurate than the next but would have to say the Kimbers have been the most consistent one hole group rifles with factory ammo.
I always start with factory ammo in my builds and then start handloading from there.
My Gunsmith says the LAW action is one of the best made action he's seen ?
Also says the Kimber is a close second, and the Tilka action is top notch.
He says the worst actions for being out of square are late model Rem 700s and Mark V Weatherby's
The nicest or smoothest action I have is the Defiance Rebel and the Stiller Predator is also very nice, but if course for the price of them they should be.