What is the best place to move your capital?

[Bogdan]

In terms of numbers. What should i be looking at?
Thank sirs/madams.

[Kimlin]

Duchy capital that has the most holding slots in your realm.

[shiggies713]

all other things equal, the province/duchy that has the highest development.

There are other things that come into play, like as India I moved my capital somewhere around the Ganges River so I can get Lord of the Ganges title, despite having slightly more developed provinces elsewhere.

If you have really high stewardship, and have 3 duchies worth of provinces, but only 2 duchy titles (to avoid diplo penalty with vassals), you want it to be in one of the duchies you actually have the title to so you can take advantage of the duchy building, and also ideally a religious holy site and its building.

Or like London makes a better capital than the de jure capital of England for example because of the special building and the sheer number of baronies within the duchy.

[D34DLY]

i look for counties that touch a lot of counties around them. if you have your capital have the highest development, it will spread that development to adjacent counties. So, a capital that touches 7 counties will help develop 7 counties.

Also, you want capital away from easy access, harder for enemies to reach. Likewise a fort with higher defense level.

Also, there may be gold bonuses, so a county that produces more gold will benefit more from the capital bonuses.

There are also cultural bonuses to consider.

[D34DLY]

and if you use mods, try the "always move capital" mod.

[Dumah]

County at farmland terrain with maximum amount of holdings that could be filled by either temples or cities depending on your religion.