From what I know...
Well...Asians are out of the question since they're illegal in the USA
Silvers are the cheapest, most common, largest, and not as aggressive as some other Aros
Blacks are more expnsive, haven't seen them around as much, maybe a little smaller than the silver, hear that they are the least aggressive of the Aros, and loses color as they grow
Jardinis are pretty expensive, smaller than the South American Aros, closest Aro that resmbles an Asian Aro, and are the most aggressive Aros
Leithartis are very expensive, hard to find, kind of like the Jardinis