Dont get the exo terra. They are too over priced and I dont like em. I would go with the black hide box's I posted before. As for size if you read the description of the hides the medium size on says "Ball pythons up to 700g" and the large says "average size adult Ball pythons". So which ever one fits your snake.

Good luck, Dont for get to buy 2 for each snake that needs hides!