Mornin JD,
I don't have a lot of info but I am in the process of starting to research the replacement of my old oil boiler. I like the baseboard heat as oposed to forced air. I also have a old indoor wood boiler in the celler next to the oil boiler which I like.
I have heard that of the few high effiecency oil boilers out there they are not working too good and was recomennded to go with a regular 85-87 % unit and a chiminy. In new construction the cost of a chiminy would pay for the upgrade to propane.
I am leaning towards propane. Propane is more expensive but the higher efficency will bring it closer and less maintenance, cleaner. If you buy your own propane tank you can shop arouind in the summer and get a better price per gallon.
Some of the new indoor wood boilers are fairly efficent but $, around 7,500.00 plus you would still need a backup boiler, oil or propane. The solo combo units are not that efficent.
I still have a lot more research to do. Please forgive my spelling.
EDIT: I missed the natural gas - that is probably better than propane.
Larry