Quick note: This does not mean to just complete with 3 star rating (gold).
The most problematic one is level 3-10. To "Perfect" the level you need to make sure Hercules' health remains at 100% and there are no errors in collecting the items. (be careful of the red mushrooms and red berries as there are a couple of each and can look similar).
The other level I have seen people say they have issues with is level 2-10, just make sure you collect the last boulder prior to beating up the bird as I hear it can be 3 starred without collecting it.
Edit: Grammatical corrections.