Get the largest cage you can afford that fits in your space. They will be most healthy and happy if they have enough room to fly and several perches of different sizes and shapes to choose from. Make sure the cage is intended for parakeets with narrow bar spacing.
myself i would get a large one becasue they will grow in to it and want more room. and that way you can put alot of toys in there to give them samething to do. i even hang a bed in the back of my cage for them,they love them.
As big as possible, making sure that the distance of the cage bars from each other is an appropriate size for parakeets. Try to get one with mostly horizontal bars so they can climb.
