Hi fellas, as above just looking for some advice on brush heads and what the main differences are. Some of these questions are bound to sound dumb but please bare with me!

Firstly I am using a Vikan square brush that came with my trolley system. Is this a good brush for everyday use?
What is the difference between square and oval brushes? Are there different types of jobs/windows that oval shape suit better for example?
Also sill brushes, are these to be used only on the sills or can they do just as good a job on the windows. (I'm guessing that you wouldn't use these on first cleans however?)
Any other advice you can give on brush heads would be great as I am new to all this.
Thanks, Tom