I struggle finding "the perfect" smooth brushes, so this is the closest I'm satisfied with.
Demo:

How I use it:

Remember:
Large brush +/or light press = soft edges, perfect for blending
Small brush +/or hard press = hard edges, perfect for harsher details
Use them interchangeably for the best results!

I always switch the colors I use on the weel to offer different color variations

Brush