It's a pity, guys, that no one thought about the fact that manticores can fly. When you take a city, they are more useful than all the "walking" units. Wyverns too. Besides, wyverns can actually be built at the very beginning. And if their rare poison works, it will be quite unpleasant. And the cyclops archers shoot.

But still, the Dark Knights are indeed the strongest. There can be no argument about that. Fast, curse, double damage, powerful combat abilities - all this makes them the strongest at level 6.
Well, unicorns will also work. Blindness doesn't happen that rarely, and that's why they can be very annoying sometimes. In general, everyone has their own quirks, but the Dark Knights are the strongest.