There is really no such thing as a first "good" arowana because most of them require the same level of care and in my opinion they are all "good", but aggression is a different story. From a beginner stand point you have two options a jardini and a silver, since these are the most common and cheapest arowana. Jardinis are more on the aggressive side as to silvers the more semi-aggressive side. Its really up to the aggressiveness of the tank mates you plan to have. Also jardinis stay smaller, so you might want to take that into consideration. Once you get the hang of keeping one and can aproprietly house one, you can move on to the more expensive types.