I feel like it depends on which level range we are talking about. If it's 1-42 archers (granted the opponent doesn't have extenders), 43-60 its fighters, at 60 mages start to rival fighters, and from there on its a give and take between fighters and mages.
Yeah fighters and mage are definitely the PvP classes, but the outcome depends on how much money you spend on SC and how good your gears/build/play style is.