Size and shape of a mascara brush, and density and flexibility of the bristles are important when choosing a mascara. The formula is relevant, but they're all similar and the brush is what really defines a great mascara. Depending on your needs, eye shape and lash length, the right wand is necessary. 

Buxom Lash mascara is my favorite. The hourglass-shaped brush has long, closely packed plastic bristles that evenly coat your lashes without clumping. Want length and drama? You will love Buxom Lash. For a more natural look, start at the lash line and work your way up (or down), applying layers until you've reached your desired thickness. This will create a curled lash with more definition at the lash line. I focus on my outer lash line and apply less as I move towards the inner corner of my eye. For thick, dramatic lashes, apply one or two coats on the ends first and then apply to the lash line. Love to layer coats of mascara - this is the brush for you. 

The larger your mascara brush, the more difficult it is to reach the outer lash line and coat your bottom lashes. The micro wand is perfect for coating 'every' lash. Before applying my volumizing Buxom Lash mascara, I apply Intensifying Long-Wear Mascara by Bobbi Brown at the outer corner of my eyes. Heavier mascara at the lash line and outer corner creates drama and intensifies your look. 

Want thicker, plumped lashes? Try a large, dense brush. Oversized wands pick up a lot of product and thus allow you to apply more product with every sweep. Wiggle the brush at the roots, so the fibre bristles can wrap around your lashes for 360° coating. This method will seriously plump your lashes and create major volume.

Tapered wands are a two-in-one brush shape. The densely packed fibre bristles and thick base will plump your lashes. The skinny tip allows for more precision and coating those hard to reach lashes.

The curved brush is shaped similar to your lash line and allows for even coverage. This brush is great for curling your lashes. 

A Spiral brush or curved bristles grab onto your lashes, coating every little hair evenly. You can create serious volume with the style wand.

I had never seen a Round brush until Givenchy's Phenomen'Eyes mascara. I love this mascara and the brush is excellent for precise application. You can focus on each section individually, rather than the 'all-over sweep' you get with tradition brushes. The round brush is also great for coating the outer corner giving you a more dramatic look.