RE: most accurate 30-30 cartridge brand
Ditto...
My Marlin .30-30 seems to prefer Winchester Silvertip 170gr over everything else. I tried Remington, Federal, and even generic reloads from a gun show and got the best groups with Winchester Silvertips.
Each rifle is unique. One will like a certain flavor of .30-30 ammo than the next - even if they are both the same make/models of rifles.