For me, it's a draw between Dawn Crosby (R.I.P.), Monika Edvardsen and Agnete M. Kirkevaag. Since I like each of them for different reasons, I can't put one of them above the other.
As regards Dawn Crosby, I love the anger she expressed on Détente's "Recognize No Authority" and the haunting multilayered/-faceted vocals on Fear of God's "Within the Veil". In the case of Monika Edvardsen, I love her original, experimental and crazy vocals, especially on Atrox' "Contentum" and "Terrestrials". As for Agnete, the only one still active among these three, I like her soft clean voice as well as her powerful and aggressive (yet usually also still clean) voice very much. My overall favourite Madder Mortem-song "Resonatine" is probably the best example because of the change of dynamics as regards the vocals (as well as the music), though I think "Where Dream and Day Collide" and "Hangman" are also good examples to illustrate what I mean.
Maybe I should also include Dominique Lenore Persi. Even though her extreme vocals sometimes are on the verge of what I can listen to, I like her "normal" voice very much.
And just in case the term "front man" in the initial post was meant to explicitly exclude female vocalists (which I obviously tend to prefer to male vocalists), I'll pick John Arch and Johan Längquist.
