IME, the males will flash for various reasons; if excited, to show off for the females, and to display agitation or annoyance with another fish.
Some species can tend to fade a bit in the absence of a female.
As far as which is the prettiest, as stated it's a matter of preference. If money isn't a main concern, check out the lineatus fairy wrasse. IMO, one of the showiest, even more so than Scotts.
In a 75, I'd look at a group of flashers. One male and three females. The fairies are a bit bigger and more boisterous to keep more than one or two IMO, unless the system is larger.