But to answer the question, I use these Dynasty brushes from Blick Art Materials. They're cheap, so I can abuse them; they have all the characteristics that feel comfortable to my hand (my hands are small) and the right amount of stiffness.
Brush CleaningIf your brushes get too stiff from leaving them out too long with acrylic paint on them, leave them in a strong solution of Murphy's Oil Soap over night.
I did not come up with this brush cleaning technique. Various people have told me about it, and I have discovered that it works. YAY!