I use them both. Bone shield offers a good group synergy. Champ points make a difference also.

Both absorb all types of damage now, and on my dk tank both have close to the same value on self. The question boils down to what you need. Igneous shield restores your stamina, instantly puts the shield up on those nearby, buffs your healing done for when that's useful, and triggers the dk's minor weapon damage buff for those nearby, as well as costing magicka. Bone shield cost stamina, so I find it easy to keep up with heavy attacks, the spiked shield morph can return some decent amount of damage, and the shield placed on allies is stronger. That secondary shield does require someone else to trigger, which is helpful for all things that proc off of synergies, but is also less reliable. Honestly it mostly comes down to preference and what you need out of the skill.