the mystery wrasse got a few votes in this thread. but here's a little anecdotal evidence which may help you decide
against one. my mystery wrasse is one of my favorite fish ever, but it is a nightmare for crustaceans. it got to the point where even the hermit crabs would only come out at night once the mystery wrasse went to sleep.
my mystery wrasse is now in one of my cousin's tanks, but in the year that i had it, it ate:
500+ grass shrimp - what most people incorrectly call ghost shrimp (wild caught, and intended as a food source)
100+ baby Gulf shrimp (wild caught, and intended as a food source)
150+ peppermint shrimp (wild caught, and intended as a food source)
20+ porcelain crabs (wild caught,
not intended as a food source lol)
1 pistol shrimp (wild caught, also not intended as a food source)
1 emerald crab
2 sally lightfoot crabs
1 baby blue crab (illegally wild caught

)
1 fire shrimp
several dozen other various wild-caught crabs
so if you value your CUC, perhaps you should think twice about a mystery wrasse. true, it is reef safe in the sense that it doesn't eat corals (duh), but mine certainly is NOT invert safe