They mean the same thing. I think "He hates my guts" is more informal or even something that a child is more likely to say. If the situation is a serious, adult situation "He hates my guts" would sound a little off. "He hates me because the boss gave me the promotion." (It would sound funny to say "hates my guts" in this situation.) On the playground at elementary school, a young person might say, "I hate your guts because you told the teacher I cheated on the test."