Those 2 angels look more impressive, especially since we can upgrade them in the Fortress just in time for Nila's arrival. You can also try using an Archmage, but I don't see the point, as the buff from angels and Archmages is the same.
Regarding your screenshot: what magic does our unit and the enemy unit have? If the enemy doesn't have Haste, Prayer, or Slow, which we can't remove, then the obvious solution is to attack it with Nagas using Wait. A speed of 8 against a speed of 4 should be more than enough.
The opponent has Haste, a cloak of speed, 2 rings of the wanderer, and stats of 99/99/0/0.
We have 5/5/2/2, and the only spell we have is "Sacrifice," and we also have the Sphere of Vulnerability.