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

I didn't read the thread from the beginning (to be honest, I was too lazy), so I don't know what you're talking about – are you referring to the appearance or the strength of the troops?
If it's about the appearance, then I definitely like Sylvan (and the music there is the best).
If it's about strength, then either Haven (due to the strength of its units) or Necropolis (due to the ability to amass a horde of vampires with a powerful necromancy skill – although it seems they nerfed this with various patches and add-ons, but I haven't played them; I only played the original version in English).