Which type of membrane protein is most likely to be a hormone?

The right answer is peripheral protein.

A peripheral protein is that membrane protein that is bound to it by non-covalent (weak) bonds so that it is easy to separate it from the membrane by solubilization by subjecting it to a medium with a high salt concentration (eg 0, 3M KCl). Peripheral proteins are found both in the extracytosolic domain of the membrane and in the cytosolic domain, although mostly in the latter. The concept of peripheral protein is opposed to that of integral protein.

you need more balloons