I prefer small groups just because a 4 member group is so much easier to stan. I also find it much easier to get to know the members really well in a short amount of time.
I feel like a bigger group is more fun coz theres loads of interactions that can take place, games become more chaotic etc etc, but it becomes more difficult to love everyone equally or to learn names.
So because of that, I think I prefer smaller groups. 4-7 is a good range