String theory is a lot of things, but comparing it with intelligent design is unfair. It is an unscientific math-fu that you can't call a scientific theory, but it is a mathematical theory. You can't explain anything in the universe with it, but you can create a model that resembles it, and tweak the parameters to look into an imaginary sister universe. What you can do with intelligent design? You can't even imagine intelligently designed world with it, something that science fiction does well.