I happen to love goldfish and advocate either housing them in a 70 gallon or larger tank, or possibly putting them in a backyard pond (that was built specifically to house them, not just dump them in some random one and leave it at that). I have 10 goldfish in my pond and I love to watch them swim lazy circles and see their lovely tail fins flow behind them. Its very soothing.
Goldfish are, to bluntly put it, garbage trucks. They will eat anything that will fit into their mouths, and poop it out tenfold. I have a heavy duty pond pump to help filter out the waste and such, and clean it out regularly to keep it flowing cleanly.
Remember, goldfish can and will grow to around 10 inches (sometimes more) in length and need a lot of space. Also, Goldfish like it nice and temperate. If keeping them in a tank, then a water temp between 20 °C (68 °F) and 22 °C (72 °F) is recommended.
“The day the power of love overrules the love of power, the world will know peace.”
― Mahatma Gandhi