The question you're asking really depends on what tank you're putting the peacock into. For example, if you have, let's say, a mild mbuna tank with labs, etc., and want a splash of color,then you'd want a peacock that could hold its own -- Eureka Red or Lwanda generally would work well. If you're looking for a peacock mild enough that you could have several males in a species only colony, then, hands down, go for the blue orchid or the sulfurhead (maylandi).
I have a species only blue orchid tank with three fully colored and mature males and five females in a 45 gallon! This was based on the recommendation of a respected online breeder and it has been a fabulous tank. Zero violence. Zero illness. Several females have held but the babies don't last (the tank also has six lucippinis.)
So my favorite at the moment is the blue orchid, although I'm a total sucker for a nice ruby red!!
man theres so many awesome peacocks why not just do an all male tank and get many different kinds... thats what i did... too many peacocks too little space lol.. i think right now my favorite is my walteri.. but i also just got a really sick lookin red top Lwanda... but im sure the 2 blue orchid juvies and the ngara flametail juvies i have will climb quickly to the top of my list when they get big and get color