Knightly Orders

Is it better to have them in a city or a castle? I mean the knightly guilds, like teutons, templars, hospitallers, santiagos...

As far as how they operate it doesn't matter as far as I know. Personally I prefer city simply because it gives a city access to heavy cav, something most factions cities don't have.

I prefer cities, so my castles have the "guild slot" free for the swordsmith guild