I got 2 oscars, also thought i did not like them before i decided to try a pair. Now they are in a large tank with an 8" jack dempsey, geophagus, heckelli, polypterus, a clown loach, a green terror and a pleco. They are probably the most playful fish in the tank, always moving, look great. They eat like pigs, will eat live food until their bellies are twice the size of their body. Up to now never seen ANY sign of agressiveness...
Oscars are not agressive fish...they just constantly eat, and constantly want to eat more.
Want aggressive? Try a pair of Frontosas in a small tank...I did that (yeah i know, they are in a 130g now...) and what a mess. Both survived tho, took one of them 2 weeks before coming out of the stone works...