What type of acrylics and what colors are you painting? Some colors (lighter), and brands streak more than others, no matter what.
I have yet to find a yellow that will cover opaquely with no streaking on the first coat hand brushed. Especially without a white base coat.
That being said, I prefer red sable brushes. And with acrylics, since they dry more rapidly, it is critical to keep the bristles slightly damp/moistened to improve paint flow. I have not had much good luck with synthetic bristles when using acrylics. Although they do keep their shape better for precision work.