TBH, ANY class, right down to the new ones in ACG, works for a villain... EXCEPT the Fighter.
I'm sorry, but the Fighter just doesn't scream "BBEG" to me. All the other classes have something related to their backstory that can lead to being a villain.
Barbarian, Bloodrager and Skald: your typical tribal leader/warchief
Bard, Rogue, Brawler and Swashbuckler: your typical gang/thug/guild leader
Cleric, Paladin, Monk, Inquisitor, Oracle, Shaman and Warpriest: your typical religious leader
Druid and Witch: your typical witch doctor
Ranger, Gunslinger, Ninja, Hunter, Investigator and Slayer: your typical assassin/bounty hnter
Sorcerer, Wizard, Alchemist, Summoner, Magus and Arcanist: your typical evil wizard/arcane spellcaster
Cavalier and Samurai: your typical warlord/commander
and then there's:
Fighter: your typical soldier/sellsword/mercenary/guy who just knows how to wield a weapon and that he's pretty forgettable... kinda lacking here...
Look, the ONLY way to make the Fighter a good villain is if you're just about to face the master gladiator, similar to the Black Duke. However, the Fighter lacks any kind of ability that define him as a villain. The only thing that could define the Fighter as a good villain is the weapon he wields, but again, so can have any of the martial classes.
My opinion though...