If we're going back a few years, I'd have been shocked that you could use brushes to apply makeup. All I used was my fingers, resulting in badly blended eye shadow and that awful mis-matched foundation. Yeah, not a good look. Ever since getting my hands on a few Real Techniques brushes in early last year, I've been completely converted. My favourite brush of all time is the RT Buffing Brush that came out as part of the Core Collection. I'd happily pay more than what I did for this brush because of how amazing it actually is. Because it's synthetic, it doesn't soak up loads of cream/liquid products meaning it applies foundation like a dream.
I'm also a lover of the RT Domed Shadow brush that I actually use for concealer. It's the perfect density and again, blends cream/liquid products like an absolute dream. The Base Shadow brush is another favourite. I'm a bit hesitant to spend £20 on the MAC 217 brush and for me, this is very similar. I use this to apply products in the crease and the shape of it makes eye makeup look flawless. For brows, I love to use the Angled Brush. All of the RT brushes are so easy to clean, cheap and easy to get. They're amazing, and if you can get hold of them, make sure you give them a go!