Transports carry around all different sorts of cargo, from common ores to precious minerals. In general, the better the transport, the more lucrative the goods it carries. All transports come equipped with guns, come with escorts, and have heavy armor. The higher end of transports have quite good guns, very good escorts, and very thick armor.
Big and slow, mounts dual positrons. You won't find one without escorts, unless someone already killed the escorts. A simple attack roll works fine, though it takes a long time.