I have to say I own a lot of Mac brushes and now have quite a few Sigma brushes and I love them just the same! SIGMA BRUSHES :: Dupe List for Mac Brushes. I have a bunch of both, and it is true, they ARE great dupes.
Favorite MAC brushes - my must haves for blending 217 and 224 are terrific blending brushes. 226 is awesome for applying color perfectly in the crease especially when you are applying product on someone else. Works well on most eye shapes.