There all beautiful, I like naso and powder blue,and I think if you do start them out in a small tank its ok, but at some point you really have to get proper size tank.
I like blue the best, but I have black paint on mine it hides powerhaeds better. Oh and I dont clean the back glass it has all kinds of things growing on it.
I change things around in my tank if I don't like the way it looks.Your tank is 6 months old ,it takes time to devlope. You can also find a store that will exchange or trade fish & corals with you.