MAC 217 brush has been around for years and is very popular among makeup artists and makeup lovers alike. It's officially called a blending brush, but it's really more than that. This brush is one of the best multitasking brushes around.
The brush head is made out of white goat hair. The bristles are dense enough to apply color, and at the same time, soft and fluffy for excellent blending. I use the 217 to apply powder and creams, including concealers, and I find it to be very effective with both products. I use the brush to apply and blend eyeshadows on my lids as well as on my crease. The oval shape and tapered tip is very useful when applying color on the crease and outer corners of the eyes. When it comes to blending, the 217 is great at blending two colors together as well as softening the edges of eye makeup. I use small circles or the windshield wiper technique to blend.
I've said it before, if I'm to keep only one brush from my collection of eye brushes, I will choose the 217 as I can do my entire eye makeup using only this brush. There are a lot of dupes for 217, but I have not personally tried any of them, so I don't know how they compare. The Office Chic made an excellent post comparing MAC 217 with dupes from other brands, you can read her her post here.
If you are looking for a blending brush, I recommend you check out MAC 217. I've had mine for a couple of years and it's still doing great despite being one, if not the most, hardworking of my brushes.