Bigger is always better. Bigger means faster growth and a healthier fish. It also means less work for you as the water params won't swing back and fourth. But in my opinion, one of the biggest reasons is money. Setting up tanks is expensive, ESPECIALLY big tanks. I spent over $2,000 [not including the tank or stand] getting everything to make my 325 gallon an amazing tank and that wasn't even with expensive lighting or gear; I mainly built everything myself.. including the filter. I'd say just buy a big tank now and save yourself the trouble down the road. Even if you resold the tanks after switching up you'd be losing a ton of money, tanks do not hold their value. Ex: my 325g new costs $3,000 + shipping.. I bought it and a stand slightly used for $600 + Gas money to go pick it up. Id even say, whether money is an issue or not, larger tanks are WAAAAAAAAAAY more fun to look at and to aquascape. You'd also need to do fewer water changes and tank maintenance after the initial set up. But in the end it all boils down to the happiness of the fish and if you have the ability to give something you might very well keep for 10+ years the biggest happiest home you can, then why not?
