The Colleseum
I have a 55 gal tank, at one point in time i had a paku, oscar, 2 dempseys, 2 convicts, green tera, talipa, sevrum, and a pleco. for a few months, it was alot of fun to watch, but as the pacu got bigger (they grow regardless the size of tank) he seemd to become cramped and angry. at first he would pick on the smaller fish and then dtarted to become incredibly aggressive toward the oscar. i had to remove. once he was gone, with the right amount of food and cleanings (once every other week, no more than 4) it was very enjoyable.
pound for pound, the convicts are the best, they can really hold there own and do breed very easily. the dempsey is the most durable and docile. the terror, talipa, and sevrum just went about there business. you need to keep this tank clean though otherwise you run in to all sorts of problem. and if you feed feeder fish, dont over do it.