I use the second one in from the right for bronzer. It's just a normal soft sable blush brush. I have a different one like kbell posted that I use just for blush.
I just use a big fluffy one from Estee Lauder. I also use the same one for loose face powder- I guess that is a no-no? Should you use separate brushes?
elizat, I use the same one for loose face powder too. I like using a big fluffy brush because it doesn't pick up too much of the bronzer so you don't have to worry about looking too orange.