When getting a new fish, it's best to have a tank. But which one? As it can be a tough decision, I have made this thread to help.
You may not believe it, but males should have bigger tanks then females. Why? Males are solitary, meaning they are used to more space as they don't share it with other fish. Have a tank the size of a Living World tank or up. If you breed your fish, please have a separate tank for that as your betta's can be territorial.
As your females aren't always solitary, a good sized tank will do. However females can fight too, so taking the risk of putting two females is not recommended. Like males, one female should have a Living World tank or larger.
If you are breeding your betta's a separate tank can lead to a better chance of eggs. Add plants and perhaps a background to your tank. Don't clean out the bubble nest, it could have eggs in it. The size should be exceptional, big enough for both to mate and lay eggs.