In this video, a guy explains why you shouldn't keep Oscars. His reasons are
1. They rearrange your tank
2. Feeding them is a chore
3. they're aggressive
4. it's hard to find tankmates
5. they need a huge tank
6. You need to do a lot of water changes
For number 1, yes they will rearrange your tank, that's the beauty of them. It's funny to see them rearrange tanks. If you don't like that then you can just not decorate your tank very much, if at all.
For number 2, no, feeding them is not a chore. Go to a local bait shop and pick up some night crawlers, me I can get 24 troutworms for $5 or 12 large night crawlers for $5, go on amazon and pick up some pellets, it's a lot cheaper on there. Go to your grocery store, pick up the cheapest seafood meat (as long as it isn't oily or anything), it could be scallops, tilapia, clams, etc. Go outside and look under rocks and you can get some worms and bugs for them. Go to your local stream and pick up some minnows and crayfish (if that's legal in your area and if you're allowed to do that). Feeding them is AWESOME, I love'd feeding mine when I had them.
For number 3 and 4, yes they are aggressive and yes it can be hard to find tankmates with them. You need to get them when they're both young and have them in the same tank, but separated from eachother so they get used to eachother. You can keep them with so many things, red devils, green terrors, jack dempseys, bichirs, larger catfish, arowanas, gars, flowerhorns, etc. It's all trial and error, but mine have gotten tankmates fine
For number 5, no, you don't need a huge tank. A 55 will work, but a 90 would be perfect for an oscar, no problem. You don't need a huge tank like he was saying
and for number 6, yes you do have to do a lot of water changes. Doing water changes is a part of having large fish. It's not that hard to do water changes.
