I hate the cakey look of foundation, so to keep my foundation looking natural and not cake like, I start off with MAC liquid foundation and use Mac's flat foundation brush 190.
I use this same brush and love it. I bought it a couple of months ago with MAC Studio Fix liquid foundation. Previously I had been using my fingertips to apply foundation. The foundation brush gives a flawless finish, in my opinion. After I started using it I had co-workers coming up to me, telling me what great skin I have LOL!