Best kingdom/province for defense?

[ShadowFox]

Does anyone have a province in mind for the best or easiest to defend against overwhelming odds? I would imagine getting pavise crossbowman 5 inside and an 8 marshal army in a 4 castle province would be the "strongest" but I don't know if there is a particular place that lends itself to be the easiest to protect. I thought islands at first because the travel speed is slower but then people can land right next to your city and siege it without taking barely any hits from the town or castle. Maybe somewhere with hill forts for the slowing effect?

[Lateralus]

It’s difficult to suggest this specifically because the map special features are randomised at each campaign start. My ideal defensive province would have 3 or 4 castles and a hill fort. Then I would build the main military buildings.
But anyway the best way to avoid wars is to hire two diplomats in the early game and then improve relations with most kingdoms except for a small one that you want to conquer next.

This approach is more effective than any other strategy that I’ve tested. And then a little later, when you’re ready, you can create the war you need through alternative means, which is part of the fun.

[DNLH]

I'm not sure Pavise Crossbowmen would be the best, I imagine you want a relatively small kingdom and they cost a lot of gold, both to recruit and replenish. I'd imagine something mid-tier, that is easier to replace, would be a better choice.

Geography-wise, I'd look toward Africa, maybe? Not a lot of settlements, but long travel times, as there's some huge provinces. I'd say islands are an interesting bet too, with Navigation-oriented Marshals and Traditions, relatively cheaper units tend to do better when fighting on sea.