Silver Dollars are cool. They have good personality, Those spotted ones are real nice. I have 6 big silver dollars, and they are real friendly. Make sure that the diet is very varied, I get kelp and seaweed occasionally and they love that. I also give them pellets, sinking algae, flakes, white fish and market shrimp, and they love to eat the feeders too.
I'm pretty sure they'd eat garbage if I put it in there.
Good luck with them!