Merchant Republics: Which capital is better, City or Castle?

[Urloc the Great]

I'm not quite sure wether to stay with my city as capital or to switch to the kingdom capital which currently is a castle.
On the one hand the castle would provide a much higher fort level for the capital, because even with the city arsenal of a republic, you only get a max of 9.5 fort levels (6+3.5) whereas a regular castle can easily get 11 fort levels. Plus you get whatever building bonuses you get from the capital for your retinue and mercs, which is much higher for castles than cities. Cities don't have access to the cultural building line.
On the other hand I already built up my current capital. And replacing one directly controlled city with a directly controlled castle would mean I would get less taxes, less eco tech and less tech spread.

So which capital should I chose for my Merchant Republic?

 

[majdavlk]

castles if you want safety for your court

city if you dont want a castle in your demesne. will make it easier to hold another city for higher gold income

if you care about retinues, i would suggest looking into a nomadic holding, if they are fully built up, they have large bonuses for all troops, but exceptional bonuses for cavalry