MarcoSac:
Speaking from the consulting perspective, it is going to be very difficult to get in without either. I would argue that extracurricular activities are more important.
It is very hard to get internships, especially before your junior year in college. Any internship pre-junior year is likely because you qualified for a special underrepresented minority program or you had some sort of connection. Plus, let's be honest, there is a limit to what you can achieve in an internship given their junior level and short-term nature. Also, the reason you are being accepted on a deferred basis is because the expectation is that you will gain 2-3 years of full-time work experience before starting your MBA. That's where the real value comes into play.
Extracurricular activities, on the other hand, can really showcase a candidate's ability to bring about meaningful change to an organization or a community. They are much more geared towards student leadership and responsibilities, and therefore can be a much better representation of a candidate's ability to be have an impact on their MBA program.
I am sure you will get a range of opinions, so good luck in your research on this topic.