This was a cute thread. Im sorry I missed it in all its heat way back when, really
I voted ENTJ and ENFJ in the end. Though I feel INTJ would do a marvellous job, they would grow weary in the end as their preferred position is behind the scenes, ime (My own INTJ often gets forced into positions of power to clean up the mess, but once that has been taken care of, he tends to train up someone to take over for him and maintain shit, so he can just do the adviser/puppeteering thing). I think an extravert would feel less burdened by the job.
ENTJs, provided they arent too ego-consumed to realize they need help and that being disagreed with isnt an attack on their authority, would be brilliant at it, I feel. They can take swift action, dont shy away from big projects, seem to have endless energy to fix shit (and lets face it, a kingdom needs constant fixing and developing), and would, if not suffering from paranoia, be open to sound boarding their ideas and their vision off of their advisors.
Wrt helping an ENTJ monarch with that paranoia (often stemming from inferior Fi), I'd suggest an NFP/NFJ Queen, someone who can help him figure out how to trust himself and others, as well as someone who is not driven by power and someone who shares that abstract vision of the world with him, to facilitate communication. That way the ENTJ *knows* at least that he can trust *one* person in his entourage, someone who is skilled at reading others and figuring out who else is trustworthy in that entourage (aka figure out the social politics of it all), which will do a lot for his sanity and consequent actions in his role as monarch
ENFJs would work similarly, though the mix of advisors would have to be customised to fit their particular strengths and weaknesses.
Personally, I'd prefer an ENTJ monarch, with an INTJ right hand to ensure smooth running of the kingdom. Aside from that, an ENFJ PR-rep, in order to keep the monarch in tune with the people, as well as keep his star rising. INFJ and NFP advisors to bounce plans off to highlight what social/personal problems his plans potentially will cause in the long run (my INTJ does this wrt his personnel for instance in his company), and which pieces of the social puzzle he missed. NTPs for the development of ideas in specialised key parts of the plans. STJs to keep track of the details within the plans, and maintain those parts already finished (external logistics), and getting updates on how things are going, SFJs for smooth running of the Castle (internal logistics), STPs as the military advisors. SFPs for minstrel duties (spreading culture throughout the land) as well as the court jester who gets to say things to the monarch nobody else can get away with, and provide him with vital feedback from the people
I also personally think that for a group unified in a cause, be it cultural, ethnic or linguistical or social in some way, ENFJS would be better suited as then that tribal element becomes more prominent and usable, something Fe is infinitely more suited for than Te.
Going further, I think that if you go down to tribal status, ESTPs would be the ultimate Chieftains, especially when strength, adaptability and immediate action wrt your immediate environment are essential and the banding together can save your lives.
Lastly, I think cities are best run by ESTJs, due to the loss of that tribal element, while still being 'small' enough to keep planning and running it on a concrete rather than abstract level, and stickler little details actually become vital to the success of said city in all areas.