I had two fem and two boy black mollys at one time but they're like puppies, anything goes in the water they'll sniff and bite. For me its just a little too much playfulness in the tank.
Buck (had two males, so stupid they used one name 'buck rogers' both from the same litter, one died) is my last molly, a baby of the last girl. He's exceptionally happy even when startled.
Has been an excellent companion to the girls tho he does tend to put on the Bar'b'que bib real quick when one dies.
There was another time when the tank was full of wysteria when he suddenly realized, after five weeks, that there were TWO blue girls! He drove himself back and forth between them for hours, I assume saying "wait, she's over here now!" the whole time. Finally they both followed him back and discovered each other, he was stunned. Wisteria can really take over a tank!