1/4" Is ALWAYS the better choice in my area because we have an occasional rattle snakeDepends on your predator. 1/4 is to keep out those that can squeeze into small spaces: weasels, mink, martens, snakes, rats, mice. It's also to keep raccoons and skunks from reaching in. 1/2 is fine if you only have larger predators, from what I've read and experienced.