For fine detail work, get sable. Doesn't have to be Windsor & Newton, necessarily; there are other brands. I've got some W&N, some DaVinci, and some other brand. I got mine through Richard Blick (take that, nannybot!), and at artists' supply stores. But it's the natural hair that provides the quality. Properly cared for, you'll be able to get fine points with a natural hair brush, and the brush will last far longer, than with a synthetic brush.
For painting figures with acrylics, I use a Nr 1 and a Nr 2 round. Though the brushes appear too large for fine detailing, they work like fountain pens-the brush holds a reservoir of color, but has a fine tip for applying the color.
For my scale modeling use, I have other sable brushes, with smaller heads, like 0, 10/0, 5/0. I use those with all kinds of paints-acrylics but also enamels and oils.
I clean my brushes with thinner appropriate to the paint-water or isopropyl, with water-based acrylics; mineral spirits, with enamels or oils; also, lacquer thinner, with enamels and oils, when paints has gotten built up in the head during a session. I don't use any fancy brush cleaners, but I do reshape the points with my fingertips, at the end of cleaning, and I will rub my fingers on my nose to pick up skin oil and then gently rub the bristles, to recoat them. There are products for that, too. I know a French figure painter who uses olive oil, to coat his brushes to preserve them.
Synthetics have their place, too. I have cheap synthetic brushes that I use for utility work, like applying a putty and acetone mixture to a piece, or applying Future, etc.