I constantly have this debate. for me it helps to decide on a category.
Africans
South American or Central
US Native
Tropical community/ planted
Solitary predator
They all have pros and cons, I prefer native because I like the tank at Cabelas so much. Ive kept Bluegill in a 55 before (babies) theyre mean but surprisingly pretty when the stress from catching them wears off. If you go SA/CA Oscars are great. In a 55g it would be best for an Oscar to be solitary predator.