Linear 1 Brush delivers a firm, precise stroke to line lashes and lips. Also defines and fills brows. I haven't used this one much. I used it to create a line in my crease and it was super easy to do. I could actually see the brush and eyelid at the same time because my hand wasn't in the way at all.
Oval 3 Brush is the ultimate multipurpose tool, with an elongated oval shape and slightly pointed tip. Smoothly shades and blends powder or cream eye shadows, powder, and liquid or cream concealer in the hard-to-reach contours of the face. I use this only for the eyes. It is so easy to blend the shadows for me.
Oval 6 Brush is ideal for blush, foundation or powder, the rounded, medium-sized brush applies, blends and contours all over the face or cheeks for even, flawless coverage. I really like using this with my MAC Studio Fix compact. The brush is so soft.
This is the nice handle they all have. It is the same for all three.