I don't have any experience with the DuraTracs, but I've had great experience with the TerraGrapplers in snow--found them to be without question far better than "Severe Snow Service" BFG ATs. Since then I've not been too keen on the snowflake rating.
Hayes - couldn't agree with you more about the BFG A/T - it's not an admirable performing snow tire on road. It's probably great in somewhat softer snow...but the rubber is too hard on the tire for cold temps and there's no siping to create lots of biting edges...perhaps one of the most over rated tires out there for snow use. My current 80 came with BFG A/Ts and the truck was downright sketchy on I70 between Silverplume and Silverthorne in icey conditions this spring. The BFG is not rated for Severe Snow Service - it's only M+S rated, which means one does not have to chain up with the BFG A/T most of the time, but it's not the same as Severe Snow Service rated tires.
The Duratrac has the official Severe Snow Service rating - the Mountain/Snowflake symbol box.The TerraGrappler as far as I know also does not have the Mountain/Snowflake symbol - only the M+S rating.
The Duratrac is the newest and most advanced tire in this category. It's based off the Silent Armor, which has re-defined what an aggressively treaded on-road
truck tire can accomplish in terms of ride quality and traction in challenging road conditions.