HIs are a bit more "arboreal" than other BCIs probably because they are lighter bodied and shorter. My cages are 4x2x2 and have branches and/or "jungle gyms" that the snakes use quite frequently. With that being said... It really is up to you what you get. I dont think that the snake would really care either way. If you are planning on a large collection and space is a real concern then the 12" tall would be the way to go. If you have the room to spare an 18" or 24" tall would be great.