The Dark Champion is indeed the most useful. It was created as an antithesis to the Champion. It is too strong compared to the Champion. The only thing I like about the regular Champion is the horse. And even then, when it dies, the sound is cool. :)

Well, the Dark Champion belongs to the advanced units. And it cannot be bought in a fortress. If you compare each of the monsters in a ONE-on-ONE battle, that's one thing, but what does that have to do with usefulness? After all, usefulness implies the monster's usefulness in the game itself. For example, in offline mode, one of the most useful monsters is the Fairy, and with ambushing allowed, it can single-handedly defeat Dark Champions and even regular Champions :) even with a numerical advantage on their side. In online play, the Fairy is also undoubtedly useful; heroes level up quickly with them, there are many of them, and they are cheap, you can build chains, you can collect minerals, and they can easily defeat slow-moving neutral creatures, even in online mode, probably. Another plus is that Fairies can be summoned if you have the corresponding magic. So, based on these considerations, one of the most useful monsters is the Fairy :) And if you compare Champions and Dark Champions, if there is a spawning location near the Dark Champion, then, of course, at the beginning, the Dark Champion is more useful, even with just one Dark Champion, you can do a lot :) However, if the game is prolonged, then the regular Champion is more useful. In the end, they will overwhelm the Dark Champion with their sheer numbers, because usually, not many spawning locations are placed on the map, and if you also take into account that the Champions will also have external dwellings and, in addition, a couple of fortresses. This is a fruitful debate :) but, in my opinion, it's endless :)

Added after 3 minutes

I vote for the Vampire))) Who else?)))

:) Well, yes, it is one of the most versatile units ;) both in the early stages of the game and if the game is prolonged.