I keep all my old brushes especially the long filberts because, over time and much use, the tips wear down and get ragged. I find these old "friends" have an afterlife for making excellent edge transitions. Another brush I really like is Langnickle's long flat, 5590 Series, all sizes. It is kind of half way between sable and bristle. While some oil painters may characterize the brush as "wimpy", I find they make very interesting brush strokes. They are excellent for edge work and for softening the features in portraits. The brush is fragile and becomes a filbert very quickly and that is a good thing.