Mediums tend to channel complete personalities rather than complete forces. While a channel might be a conduit for the cosmic flux, a medium might be a channel for your deceased Aunt Suzy, the medium’s own spiritual guide, Archangel Michael, etc. This person is aware of the personality being channeled and is versed in the quirks that may come up in a session.
Some mediums work only with spirits with whom they have a long-standing and comfortable relationship, while others seek out a specific or unique spirit depending on the client they are serving. Archangels and Saints from the Judeo-Christian paths, celebrities and personal spirit guides are common personalities seen in medium work.