I bought a round one where the trays all have a whole in the middle for the blower to move the air through. I bought it because it was a little cheaper the the square ones. After using a few times I am finding that I wish I had bought the square one. Not that the one I have doesn't work great, I just think it would be easier to get things like peas and carrots into a ziplock bag if the tray didn't have a whole in the middle.