My fave fish right now is probably my lubbocks fairy wrasse.
He is Mr Cool. Doesn't bother anyone, doesn't mind if someone chases him off from their turf. Also, is a very pretty fish that eats all the food I feed.
Without a doubt - a purple tang. I call mine "Purple Pete" and his color is pure royal elegance. I saw hundreds of them when diving in Eilat this past spring.
I really like my mystery wrasse. Very colorful and good "personality".
I know it's not a fish, but if I could maintain a tank with cuttlefish, that would definitely be my favorite. Intelligent, color-changing, predators...? Neato.