Well.. they DO make high-pressure forced air systems, but they're
expensive, and probably beyond the typical DIYer.
Personally, I like forced air more than I dislike exposed ductwork,
but since you apparently differ, I'd say a hot water system
offers the most versatility..

If you go to www.burnham.com, and click on residential,
you can look at different types of baseboards heaters,
freestanding radiators, and air-convection systems
that can do double duty as AC.