I don't think you could go wrong with either. Dimaggio lost 3 years to Military service in his prime plus retired at 36, so it's not hard to imagine him getting 500 hr's without that...yes yes, plus he bagged Marilyn and I shook his hand, so I have that connection.
As for Williams, he lost all or parts of 5 years to military service (and he was frickin' John Wayne in real life) so kudo's to him, and it's very easy to imagine him making a serious run at Ruth's HR record without that.