Apart from your personal preferences, the size of the active loudspeaker you need depends on the size of the room and the type of content you will be playing.
Larger speakers can typically produce more volume and bass, but are not ideal for smaller rooms or for music that doesn't require a lot of bass. Smaller speakers are a good fit for smaller rooms and for music that doesn't require a lot of bass, but they may not produce enough volume for larger rooms or for certain types of content.