a 6ft. dia pond would last you for years, but eventually like in 5 - 10 years you will probably have to upgrade to 8ft. or larger. As far as aquariums, if you are going to get one that is that big and are willing to pay the money for one that is 3ftx3x8, you might as well just save a little longer and get a 4x4x12 or larger. Either way if you go aquarium for it you are looking at mega bucks, and if you do a pond you can do it way cheaper, you just have that debate that everyone says they want to see their fish from the side. I personally have my catfish in a pond and find that I can pet and feed him from my hand and be closer from the pond angle. Plus if you do a pond just put a viewing window on the side to see them at that angle. Just my 2 cent.