For oil painting, I can recommend Da Vinci paint brushes because those are the ones I have been using for many years and was always very satisfied with them.
da Vinci Brushes da vinci brushes 5023 maestro 2 hog bristle flat (sizes 2,4,6,8) artist brush set, black 4
lenbicki Fan Brush Set Hog Bristle Hair 6pcs Artist Soft Anti-Shedding Paint Brushes for Acrylic Watercolor Oil Painting
Da Vinci Hog Bristle Series 7707 Plein Air Oil Painting Brush, Round Short-length With Black Lacquered Handle And Copper Ferrule - Paint Brushes - AliExpress
NEW! Art Institute 4 pc Hog Filbert Artist Brush set ONLY $3.75 each brush
Da Vinci : Natural Hog Bristle Oil Painting Brush : Series 7179 : Flat : No. 18
Brushes for Oil Painting – Stuart R. Stevenson
Da Vinci Series 7223 Maestro 2 Artist Paint Brush, Hog Bristle Extra Short, Great Spring and Endurance, for Any Type of Paint - AliExpress
Da Vinci Artist Brushes - Handmade in Germany - Welcome to Vibrant Art
Da Vinci Maestro2 Bristle Brushes – Rileystreet Art Supply
Beginners Guide: Types of Oil Painting Brushes - Ran Art Blog
Da Vinci Pure Badger Oil Brushes
Flat - sizes 1 to 30 Bristles are hand shaped and interlocking for better color-carrying ability Seamless, nickel-plated, brass ferrules are rust
da Vinci 5023-05 Hog Bristle Series 5023 Maestro 2 Artist Paint Brush, Flat Long-Length with Red Handle, Size 5
Top Acryl Flat Bright Paint Brushes – Monet's Art Supplies