I'm a BIG fan of real techniques. They have a few sets, but if you are looking for just one I'd grab the core collection (it's the gold set). It has a buffing brush, a highlighting/contour brush, a foundation brush (some people say they use more for concealer, but I find it great for the thick liquid foundations I use), and a detailer (use it as a lip or possibly liner brush). These brushes are incredibly well priced for how amazing they are! Also if you just wanted to try out one to get started in the brand (just one brush as an intro if you will), grab the expert face brush. I can do just about everything foundation and blush wise with it!