Thanks for the responses so far.
I'm a bit surprised that the vlamingi hasn't gotten more support. This would be the easiest fish for me to add... they have several of the right size right around the corner, on sale, probably won't have any aggression problems, etc.
My wife likes tangs and voted for the powder blue. I'm just not sure that the colors on this fish would add anything special to the overall color scheme in my tank.
I was leaning towards the snapper until I talked to my wife. It is locally available, reasonably priced and would probably also have little to no aggression issues in my tank.
The Pinnatus bat is awesome and a great challenge. But they do lose some of their awsome-ness as they grow into maturity and may be intimidated with my aggressive eaters.
I am now leaning towards the achilles. It's not incredibly unusual but the colors would add a lot to my tank. If I can find the right one, at the right size, I may pull the trigger on this.
But my mind is constantly changing....