These are four very similar photographs, with very slight differences between them.
Rhythm plays a key role in these photographs. The black lines of the window grid set a strong rhythm. The way the green leaves and dark butterfly disrupt, but follow this rhythm make them the focus. Balance is another key player here. The balance between the light and the dark, and the positive and the negative.
For me, I feel the lower left hand image does the best job with the balance and the rhythm. I felt the lighter color butterfly in the other images some how threw the combination out of balance.
In the lower left hand, the unbroken field of while along the bottom of the image, balances with the bright white area that balances the green leaves.
Others may disagree. My daughter for one feels the upper left image is the best. When asked why, she says because it is. Part of what makes all of art interesting is that it is up to the artist to choose which principals of design to follow.