I grow two plants in my 2 foot x 2 foot 7 inch grow space. It always gets crowded and inevitably one plant matures earlier than the other and the remaining plant does very well because it has the whole space to itself.
This only works because I’m very aggressive with LST, starting a week and 1/2 after sprouting until the start of flowering. This requires daily care throughout this period, so I can’t recommend it if you can’t commit to at least 10 minutes of daily care.
If you are lazy and seeds are cheap or free, then more plants might be your speed.
Last grow I got 8 ounces dry from two autos. I’m expecting the same this grow. 3 ounces dry from first one and I’m thinking 5 ounces dry from second which is currently drying.
Also, I’m using feminized auto seeds. If you are using regular seeds, more plants will give you a better shot at getting enough females.