I assume you are planning for life as you do with most of your fish jaws, in which case you shouldn't consider an African aro, it will grow to large, ive read they can be nippy, and are hard to stay alive since they are filter feeders, they require to be fed multiple times a day, serious dedication. I say it's down to a black and a lei, though leis are said to reach 30" though I've only seen some come close. And though blacks reach 30" as well, they're more slender and likely flexible which would be better if you have decor. Blacks are less aggressive than silvers. I disagree with the ranking system of aggression stated prior to my post. Blacks are the least aggressive by far, they get picked on by other aros, and are commonly kept with discus which are sensitive. I'd be worried for the black if you got it, it will more than likely be picked on, where as a lei would defend itself or possibly take top spot. It's risky either way, you have to decide what you want to risk. Personally I'm no fan of leis, I'd chose the jar anyday over it, but I like darker fish. If I were in your shoes I'd chose a black, for the simple fact it won't pick on anyone since you value the other fish more, where as a lei, you're kind of flipping a coin and hoping for the best.