Which faction do you like the most in Heroes of Might and Magic IV?

Are you talking about the battle in the dungeon?))

Not just that. Indeed, "Battle of Underground" is a classic example of a rush map. With the right strategy, you can break through around day 9-10 and crush everything :)
Let's just say there are many maps where having a fighter is more advantageous than not having one. This is practically any map where there won't be too much "meat" guaranteed on the "final" stage. Especially where it's fundamentally faster to break through the utopia. And in general, there are many "entry-level" strategies. Playing with a fighter is even used to quickly break through something specific, and then remove him from the army (for auxiliary purposes) or simply train him to the point of learning magic. (the assassin class is also fundamentally interesting here)
In the final stage, a well-trained fighter is good as a "shield" against direct damage magic (we've trained him for resistance), and in general, there are many other uses...
Although, I repeat, on very "meaty" maps, a slow-moving second-tier unit can be much more important than a grand melee fighter. :)