Wow - resurrecting an old thread. I'll chime in, though, since I hold a full house: A pair of 39As and a trio of 452s.
I don't know whether the OP was asking about the intrinsic accuracy of each, or which is easier to be accurate with under a given condition ("net" accuracy). I suspect that most people, myself included, can really only offer thoughts on net accuracy, since we (I) never shot each from a vice, using each rifle's preferred ammo.
Having said that, though, I found both to be accurate. My scoped 452 varmint will smoke any of the others any day off a bench. Comparing apples to apples, though, I can shoot my peep-sighted 39As nearly as accurately as my peep-sighted ultraLux when standing, shooting offhand. Off a bench, the UltaLux edges the 39As a wee bit.
Both are great rifles, but IMO, they have their fortes. For plinking, the 39A gets the nod. For bench shooting, the 452. For hunting, either would be great.