What is the right article / group for me?

To select the right format for what you need it is important to check, what you want to do with the selected title.

Do you need a format that can be played and edited on a keyboard or another synthesizer?

Then you are looking for a MIDIfile. To be able to reach the best sound you should know, what MIDI format you need. This usually depends on the device which you are using.

If you are looking for an instrumental song with or without a vocal line you will probably need a so called Playback.