gmusicapi currently has three main interfaces: one for the music.google.com webclient, one for the Android App, and one for the Music Manager. The big differences are:
Webclientdevelopment has mostly ceased, with the
Musicmanageris used only for uploading, while
Mobileclientsupport everything but uploading.
Mobileclientrequire a plaintext email and password to login, while
Mobileclientboth support streaming, but
Mobileclientrequires that the Google Music app has been installed and run before use.