If you're going just on looks I like the powder blue better. The naso is a little too much for me.
I think if it's about more than just looks, like which is harder to keep, or get ich easier etc. then the first thing to look at is tank size and what else is in there with it because so many things like aggression, eating habits, natural immunity etc. are exacerbated by stress. So for example, maybe a Naso is more likely to fight off ich in a 300 gallon tank than a powder blue would be, but in a 125 you might actually have an easier time with the blue since that's enough tank for it, but not the Naso. And anyway, ich is not all that hard to manage if you dot your I's and cross your T's with quarentine.