Anna (Noatun) Iceberg VS Luna?

What I used to do (before I pulled better green units) was run Triangle Adept and Draconic Aura. This is to boost Anna’s relatively low damage output. Additionally, draconic aura will boost damage by the same amount as iceberg, which is better on other units anyway. Boosting attack using hone and spur is easier and has better team synergy than boosting res for increased special damage. Furthermore, you don’t have to worry about tanks that you have color advantage over because of Triangle Adept.

I mean.. her Resistance isn't really that high. I only have a 4* Anna, but from her character page, she only has 28 resistance...

So unless you're using skills that drastically increase her Res stat, then I don't see Iceberg being the best skill for her.

As far as Luna, isn't that better to use on units that fight foes with high defense/resistance?

Anna with Luna would work well in battles where she fights against 30+ def foes. But anything less, she’d be better off with Iceberg.

For the 3-turn cooldown offensive specials, a good rule of thumb is if your attack reaches 50 or more before buffs, Draconic Aura is better than Luna. If one of your defensive stats reaches 30 or more, Bonfire or Iceberg (whichever stat has that value) becomes valuable as well.