Vulnerable vs Secure Ports

I was in an interview last week and was asked to give a list of vulnerable vs secure ports.

I listed the basics off the top of my head that were obvious -20/21 v 22 and 80 v 443. He didn't seem too impressed and told me I may want to prepare for this question in the next interview.

I understand that that the best practice is to disable unused ports etc.

Does anyone have any insight as to what exactly would be a good answer to this question?