If you plan to use your companion as a ranged DPS, you should always use Starfall as their first ability for two reasons.
1. Like Meteor, it has a delayed strike so whatever ability they follow it up with will both hit roughly around the same time, makes their rotation a little smoother.
2. If you see the circle being spammed it basically tells you they are not in Line of Sight and you need to move in order for them to properly attack the target.