What little I've read on this, the best brushes for your hair are ones with natural boar bristles. Apparently they disperse your natural oils throughout your hair and doesn't pull or snap your hair like synthetic bristles do. I'm pretty sure they sell them everywhere (even WalMart), but I bought mine in a beauty supply store for about $9. I think the denser brushes are good for thin hair and vice versa. I wash mine with my regular shampoo in luke warm water.
Hope that helps a bit!