The best to worst medieval king/queen, T7S edition.
Donna: The most competent. She probably was her father's advisor/secret power behind the throne at some point. Has a wide range of abilities, except maybe intrigue. She may be too unorthodox for the time, too, which would cause problems. Unfortunately.
Red: Good at war, honor, and duty, but his diplomacy is questionable. But Kitty makes up for it.
Hyde: The peasant rebellion king. Tries to implement measures way ahead of its time, and gets executed by the powers that be. Probably, unless he has powerful allies.
Kitty: Very good at diplomacy.
Eric: He's good at diplomacy, but he's awkward. He'll be a solid peacetime king, but a questionable wartime king. Since he would have to get directly involved, and he's better fighting from afar. Unless he has a warlike wife by his side. Then he'll be better.
Jackie: Is either a jack of most trades, ala Eleanor of Aquitaine, or is a desperately scheming political pawn who pushes herself into power, Isabella of France style. There is no in between. Will probably end up in house arrest or something, at some point.
Laurie: Is too conniving for her own good.
Bob: Is far too easily swayed and taken advantage of.
Fez: Same as above, but he's even more awkward.
Midge: She's just confused. A puppet.
Leo: Same as above, but he's extra spaced out.
Kelso: Is dumb, reckless, and puts his country into a downward spiral. He's only a little bit better than Charles the Mad. He's not mad, just dumb.