I don't do a lot of fancy artwork with my makeup so the extent of my makeup brush collection is tiny. For me, it basically comes down to getting the perfect base so my favourite and most used brushes are face brushes.
Real Techniques Duo-Fiber Face Brush | For a long time I used a really thick, heavy brush for applying powder. Then I learned that using such a heavy duty brush was displacing the foundation and concealer I'd so carefully applied underneath. This Powder brush from Real Techniques is perfect from loosely applying powder to stop shine or set foundation/concealer in place.
Avon Blusher Brush | First of all I love this brush because it's really soft. Second of all, it's shape is tailored to make blusher application incredibly easy. It's a bit cheaper that some of the other blusher brushes from other brands but it's quality is still top notch.
Real Techniques Cheek Brush | Again, another super soft brush. This one is a bit thicker and I often use it to either 1) blend in some blusher if I've been a bit over generous or 2) apply highlighter. It's a thick-headed brush so it holds a lot of product too which makes it perfect for applying a bit of colour whether it be blusher, highlighter or bronzer.
Real Techniques Expert Face Brush | I used to apply my foundation with my hands and it was a sticky, messy way of going about it. I eventually bought a sponge but I just felt like it ate the product and I didn't get much of a finish. Then I went and bought the RT Expert Face Brush and it transformed my foundation game. I squeeze a bit of foundation onto the back on my hand, dab my brush in it and then apply by 'buffing' in small circles. It gives a lovely even finish.
For a flawless base, I don't think you can go wrong with these brushes. Avon's brushes are really good quality to say they're pretty cheap and you know you can't go wrong with Real Techniques!