Do you prefer armor or attack?

We tested: Tazar, level 20, 10-10-1-1, with 1 Archangel, against Kreg with the same parameters, level, and Archangel; they inflict the same damage on each other!!!

If both have Attack and Defense skills, the damage is very close; for one Archangel, it might even be the same. Otherwise, Kreg deals slightly more damage. But Defense (armor) also applies to ranged combat. This example shows that Tazar's specialization is better at high levels. If Kreg doesn't have Defense, and Tazar has Attack, then Kreg hits harder.

And Tazar will also be good in defense; I tested 40 0 0 0 and 0 40 0 0, and 10 angels; attack is what matters.

You're confusing skills with parameters; they have different multipliers when calculating damage. For the parameter coefficient, the difference between the attacker's attack and the defender's defense is important. In your example, this difference is zero, and no one will get any bonuses.
The Attack skill is more effective than the Defense skill in terms of pure damage. But don't forget that in many key battles, like the one in Utopia, you are the one who takes the first hit, not your guards. Plus, it's important what troops you're playing with. For example, for the Swamp faction, Defense allows you to not lose Vipers in battles for a week, who often have 10 HP left (or even less), but they survive. But for the Crypt faction, Attack is more important for goblins, because they can't receive reinforcements; they will die quickly. It has already been said that the skills are approximately equal, depending on the situation. And you should take both.