The Cervantes Class Frigate is what I imagine a typical hero ship to be for a plausible set of independent adventurers or a small naval crew. About the size of the Millenium Falcon or the Serenity, this ship is about as small as a generally useful ship could be.
Unlike the Millenium Falcon or the Serenity, the ship requires a crew of about 30, which it can sustain for 120 days. It has an dry mass of 860 tons, and a wet mass of 1014 tons.
The Cervantes Class was adapted from the EH-800 series commercial lighter, which (oddly enough) was originally funded as a lunar assault shuttle. The massive engines were designed to facilite as single-stage-to-luna flight profile. The shape of the hull allows for powered re-entry into Earth's atmosphere. The landing feet double as a heat shield.
The project was scrapped as being deemed too escalatory. However the prime contractor (Etoyoc Heavy Industries) adapted the powerplant into a lighter. Lighters are generally used for shuttling cargo between massive vessels and space platforms.
The Cervantes Frigate trades much of the fuel volume and internal cargo space of the EH-800 for mission equipment and crew accommodations. The frigate often takes on an external drop tank for deep-space work.
Like many vessels employed by the ISTO, the Cervantes class rotates to provide the crew gravity during coasting portions of the craft's flight.