Looks are subjective, and what may be attractive to one, may not to someone else. IMO, if you want a real colorful fish, you can't go wrong with a blue face, emperor, or majestic. Neither are terribly difficult fish, given the right conditions. The majestic stays a bit smaller. I wouldn't personally keep a blue face or emperor in less than a 180, so if the uppgrade is a sure thing, those fish are considerations. A more subtly beautiful fish is the blue ring angel. Also take a look at the scribbled angel. They are pushy once they get older but striking looks. Take into consideration what tankmates you plan to keep.