My favorite brush ever is E.L.F.'s (eyes lips face) powder brush ($3). It is a flat top brush about 1.5-2 inches in diameter. It is super soft and I love pressing it against my face :). The bristles are average in density, not super packed but not sparse either.
It is very cheap and multi-purposeful. Before I used this brush I hated foundation. My foundation always settled in fine lines. When using this brush, I get a flawless airbrush look. All I do is dab foundation around my face and buff it in. It saves product too because the brush spreads foundation better. Another reason why I love this brush is because it applies blush well (this sentence is a lil like a tongue twister haha). It gives my cheeks a very natural wash of color. I like how this brush can be used on different texture of products and gives even application. I use it for my liquid foundation, blush, bronzer and matte powder :). Let me know if you like this brush too or if there are any secrets to this brush that I haven't unlocked yet!