Neither. Night mothers is better than both of them.
Only if you are the only one running it, but yes, this is correct.
Between Hundings and ashen grip though...Hundings, all the way. Ashen grip has a terrible 5 piece bonus.
PC NA AD
Gamma Fyr: Dunmer Sorcerer Stamina DPS (the Missing Sister...props to those who get the reference)
Samekh Fyr: Dunmer Nightblade Magicka DPS
Claire Le'Rouge: Breton Templar Heal/Tank (the Resplendent Bastion)
Augustus Constantine: Imperial Nightblade PvP (Blackwater Bandit)
Shadow-of-Sundered-Star: Altmer Dragonknight Lowbie
Hundings is the "standard" Stam DPS set. It is hard to go wrong with it. Twice born star is better in a perfect raid and seems to do better anytime using VMA dual wield VMA weapons.
As others have said, night mothers is also a good choice. If by yourself, you will pull better DPS than hundings. If you are the only Stam character in a group, again night mothers is probably better. In a group with muliplie Stam toons, the lowest DPS should be running night mothers. The armor debuff is really nice and applies to everyone, but it does not stack.
I tried ashen grip in the first month of the game. The fire breath did almost no damage and it interrupted my visual feed back and screwed up my rotation. That or it actually forces you into an animation cd...I never figured out which.