GW aren't bad, my problem is they don't make a small enough brush. But if you want really high quality brushes at a good price check out Windsor & Newton, and Davinci. Extremely good brushes, I absolutely love them, and if you go to coolminiornot, and check out any of the really good artist there and ask them what brushes they use. they'll say the same.
Don't get brushes from michael's or other craft stores. You need to get brushes that use kolisky sable hair for the brushes.