Depends on what you want. Livingstonii can have the cool hunter camo. Venustus are more colorful. Venustus males can really color up light blue and yellow, and keep their color well. Livingstonii and Polystigma males get dark blue and can be attractive, but don't really color up bright and keep their color like Aulonocara. I wouldn't get a male Livingstonii expecting a brightly colored show fish, even thou you may still like him. Neither are very meek for a "Hap". Venustus seems to grow somewhat bigger.
I have a 8-9" venustus. He can be very aggressive. I had to remove him from my 220 gallon because he was taking half the tank for his own with other large haps, champs, buccos, tyrannochromis. I moved him to a 125 gallon that has larger talapias and he is fine with them, no aggression.
I currently have a 6.5" polystigma and a 5.5" livingstoni. Polystigma has taken tank boss position from my 7" blue dolphin. He can be agressive at times but I've seen alot worse. The livingstoni isn't to agressive yet but I'm sure that will change. My current predicament is my 4.5" fryeri taking over half the tank from fish twice his size. Fish is beautiful but will probably have to move or re-home him
Jread002. Very interesting! Currently, my tank boss is a Copadichromis borleyi. I suspect soon my Aristochromis cristyi will take the boss position as he is growing like a weed! I have a fryeri, but he never chases anyone. Lots of unique personalities to these fish.