What is the best heating system for a threee story brick house(100 years old)?

To me it's hard to beat hot water heat with radiators. If the boiler is really old you will realize a huge savings simply by replacing it with a new energy efficient model. If the boiler is not much older than ten years , you're much better off putting your money into new windows and more insulation, then later replace the boiler.There are a few ways to save fuel with addon products. Outdoor reset controls read the outside temp. and match the supply water temp to your systems requirement based on a preset curve. A very simple thing to try is constant circulation- running your circ. pump constant during the heating season and the burner will respond to the room thermostat, injecting heat to the circulating water as needed. This drastically reduces standby losses.A relatively new product by Beckett Corp. is the "heat manager" . It's a simple to install device that "learns" your boiler cycles through a supply water sensor and is capable of just running the circ. pump and not the burner if it knows there is enough hot water in the boiler. They guarantee you a 12% savings at the least which is huge at todays oil prices. Hope this helps.