Warstomp is generally better than Hardiness in most situations, but being a multiboxer and having 5 grounding totems available and 5 separate earth shocks if you stagger them correctly, warstomp loses a little value since you'd basically only use it to get your own heals off.

Hardiness is decent when stacked with other stun resist effects, it helps you keep control of your whole team more often, it's a rogue killer, and you usually don't notice how much it helps because you're not on the other end of the stick, being the stunner not the stunnee.

Warstomp is better for most playstyles, but it really just depends who your enemy is and which classes you want a better counter against. Warstomp against casters and somewhat against melee if you need a clutch heal. Hardiness against melee, period.