Sigma Makeup Brushes VS. MAC Makeup Brushes?

I know that Sigma makeup brushes are supposed to be excellent quality and exact dupes of MAC brushes. I ordered a little sigma makeup brush kit with maybe like six brushes I think? But I was wondering if there are any MAC brushes that you would consider a must have over the sigma dupe? I really wanna have good makeup brushes becasue I know they make all the difference in the world. Thanks! :)