Best foundation brushes?

It's not always so much the brush, as it is the technique that you're using. As long as you have a good color-match for your foundation, are using a foundation primer, and are blending it a lot, and setting it with a light powder or a setting spray it should look close to flawless. Personally, I use a flat Sephora brand Foundation Brush, and I have had no issues with it. (It's identical to the Chanel brand Foundation Brush, you own, minus the name of the brand on the handle.)