Yeah, long since made that analysis for my town, and would choose the CWA hall, closely followed by the town's oldest bank and the Gentleman's Residence. All sturdy well-made stone and brick structures, multi-storey, good lines of fire, small barred windows, built to resist bushrangers, wildfires and hostile natives. Possibly also the town's original police station, more strongly fortified but not big enough for above half a dozen people.