Upgrade or alternative upgrade?

3) The Claw attack is a less predictable ability and more difficult to use. The Roar ability looks better and guarantees that the opponent won't retaliate.

Quite the opposite. The Claw attack always works if you move a certain number of squares (I don't remember exactly how many). So, I choose the Black Bears.

Since the Berserker's ability is quite difficult to use against an opponent, as your own units may be nearby at any time, and the Berserker attacks a random nearby unit.

That's also incorrect. They don't attack your own units if they reach at least one enemy. I prefer Berserkers because both units are cannon fodder, but Berserkers at least have a chance of an unreturned attack. Although, it also depends on how many large creatures the enemy has.

But I prefer Erls. With the Berserker Rune and War Frenzy, they are often more useful. It's especially nice when the opponent stands shoulder to shoulder. You hit the weakest one, but all of them receive the same amount of damage, and we receive the least damaging retaliation.

For this reason, I always choose Erls. And also because they deal almost twice as much damage as Yarls, and because their ability is guaranteed to activate on attack, rather than randomly.
I basically agree with everything else.