I thought it might be helpful to make a thread for discussing what sort of ultimate building configuration you should be working toward in any type of province. For example, I've become a big fan of plains provinces with horses because once you place a stable, the fully upgraded mill building, and a fully upgraded town council building along with the horse archer nomad guards (+12 gold for horse provinces), you've got a fantastic money generator. I've gotten them up to +50 gold per turn.

That's an easy one, though. A better question is what to work toward with regular swamp provinces that have no special resources. I like to find one with good gem production and put multiple special buildings in it to jack up the gem production as much as possible. I've gotten swamps up over +20 gems per turn by doing that.

There seem to be a larger number of swamp-only special buildings (and guards), but I'm not sure how advantageous any of them are.

Unfortunately, swamp provinces often represent a blockage in a travel route (necessitating a stable), and also commonly host goblin populations (which means popping a Deputy's/etc House down is important to keep corruption under control), so I usually only have 1-2 slots free for those structures.

For Hills with Mithril deposits Regular Mine plus the Ancient Mine + Dwarf Clan guard (+15) are always good. Also if they happen to be Dwarf race then putting in Deputy is needed.

When I play in sandbox (colossal shard, 1 opponent), I don't max first ring - some events could happen only in provinces with available building slot, like map with ancient treasury.

That's a good point. It's definitely good to have a few open building slots.