The most favorite fish we have had is based on it's personality and it has a nice color combo. We had this fish for 8 years and are trying to get another one, quite hard to find recently. That fish is a Red Sea Mimic Blenny. The best personality i've ever encountered in a fish, personable, fearless and active.
I could list many fish I think are beautiful, gorgeous or rare but so far this fish has been the closest to our heart. I am a wrasse lover and have had many gorgeous wrasses but none have topped the qualities of this fish.