No difference

There is no real difference in meaning. They both sound fine. "He's not..." highlights the negative slightly, by separating out the word 'not'.

‘he’s not’ is shorter to say and therefore more common, but ‘he isn’t’ and ‘he is not’ don’t sound wrong and could be used for effect in certain cases.

Hey J, "he's not" expands to "he is not". And "he isn't" expands to "he is not" as well. So there shouldn't be any difference between the two. I suppose one grammatic feature you should be aware of is "Andy's car" does not mean "Andy is car", it means Andy owns the car. You would also say "his car" as equivalent, not "he's car". Hope that helps 🤠