Generally speaking, my preference in foundation brushes is either for thicker and denser ones (like Cover Fx brush or Sephora #55), or stippling brushes. This is why Smashbox Foundation Brush No. 13 lives in my concealer drawer and is used mainly with liquid concealers and under-eye highlighters such as Touche Eclat, when I want to cover larger areas and make sure everything is blended perfectly into my foundation (not to mention my face). Smashbox Foundation Brush No. 13 is very soft and great for this task. When I can convince Sophie it was not actually designed for her amusement, that is.
Smashbox Foundation Brush No. 13 ($29) is available from Sephora, Ulta and smashbox.com.
Photos by me.