I have tried both and liked them. However, using MAC Studio Fix is better, I feel, for 3 reasons: there is only one step to use MAC vs. several with Bare Minerals to achieve basically the same look.
There are many more shades to choose from in MAC and just about 3 shades with Bare Minerals, so a greater chance of matching your natural skin color.
MAC is much less expensive!
The below is from MAC Cosmetics web-site. Good luck!
Studio Fix is a powder and foundation in one that combines good coverage with ease of application. Designed to be used dry, the powder and pigments create a matte, velvety texture. It contains Silica, which helps to maintain a matte finish by absorbing oils on the skin, as well as Talc to provide a smoother, less reflective, matte finish. The talc has been milled to a microscopic size to provide a beautiful texture while allowing the skin to breathe. This product is long-wearing. It is available in a wide range of colours. It can be applied with a brush, sponge, or a powder puff.
15 g / .52 oz
US$25.00