OK – Let’s keep it simple. For acrylic paint, you want to stick to synthetic bristles. Let’s face it, acrylic paint is a polymer – basically, plastic. That alone makes it tough on natural bristles, particularly if you are a “scrubbler” like me. (Scrubbling is like rubbing paint onto a substrate with your brush.)
But synthetic bristles can be stiff or soft. Stiff bristles, like Princeton Catalyst, creates texture in paint. Soft bristles, like Richeson Grey Matters, create a smoother, less textured, swipe of paint. Pretty basic stuff.
But brushes are only one of the triumvirate. The other two are paint viscosity and type of substrate.