Out of all the stock craft, realisticaly the Shuttle-A would have the best chance, as it would probably have the living space, galley, sleeping quarters, etc., that human beings would need for an interplanetary voyage. The Delta Glider may be interplanetary in theory, but three years is a long time to sit in the cockpit of something the size of a large fighter.
There are many Orbiter addons here on this site that simulate various spacecraft, most of which are suitable for going to the planets.