I have had both but my preference goes to the oscar. If you go with the convicts you will start out with two and end up with 50. They breed like I eat pizza I don't think you will disappointed with either
My O is 6" and he just randomly decided he was going to try and eat my 2-2.5" FM (I know it's not a Con but almost identical body anatomy at that age) during feeding one day. He certainly was a mouth full. He had half him hanging out and was chompin' him. I did manage to spook my O into spitting him out while attempting to net the O. The FM, besides the gnarly mouth damage from where the pharyngeal teeth chewed him up a bit, is doing fine and in a 90g grow out now.