he loved all his students, nagato a lil less because he killed him. but i will def say he loved naruto more. he was for all intent and purpose a father to him, after all he was his godfather. jiraiya even said that he liked teaching people who aren't geniuses and we all know that minato was a "once in a lifetime genius" according to jiraiya. Add on to the fact that they traveled together and he basically expected him to bring peace to the ninja world, i think it's safe to say he liked naruto most.