Either works fine, but Orc lends itself more to stamina. But I used to run my orc as a magicka tank and she had no problems, so if you prefer magicka, stick with it.

I'm running a DK tank too and recently moved from magicka to stamina, I'm not min/maxing though with 3 stat glyphs on my armor. With 25k stamina it's enough to block, taunt and debuff trial bosses, ~18k magicka for self/group support and ranged taunt and 31k health to avoid being one-shot when not blocking.

before I moved points from magicka into stamina it was easier to support the group with chains and talons but long fights are way easier now with the larger stamina pool.

Since my primary role is holding aggro from the biggest threats it is convenient to be self supporting, no need for the healer to run repentence or shards for me (although I would grab them when I'm able too). With healers throwing orbs or using elemental drain I can use the extra magicka to provide crowd control but that is not my primary goal.