I prefer a top down where project leads are responsible for code, I.e. they review all code and they are simultaneously responsible for getting things done. It forces balance. I will let juniors make a mess in certain areas and not others. Sometimes you even let bugs in if you know a specific test will fail so people are more careful and don't depend on reviews too much. If you are a bad lead and nitpick every little thing, then you get to explain why your project isn't ready. Honestly getting devs to git add -p and look over their own pr catches much of it.