More then likely it has to do with the amount of times you have previously solved a ReCAPTCHA before. If I delete Google cookies from my browser I will get the

More then likely it has to do with the amount of times you have previously solved a ReCAPTCHA before. If I delete Google cookies from my browser I will get the harder to solve ReCAPTCHAs at first, eventually it will turn into the easier ones. If you are logged into a Google property you might also get easier to solve ones, since they know you at least have an account and previous account activity.