Duke and UNC are culturally and socially polar opposites.
Duke has a high number of people fom the northeast, hence the pejorative nickname "The State University of New Jersey at Durham, and overall is not as friendly and welcoming a place as UNC.
Understand that most med schools do not accept many of their undergrads and Duke is not an exception to this rule so attending Duke undergrad can actually work against you for admission to their Med school. Incidentally, admission to Duke med requires has a lot more pre-requisites than many other top med schools look at their website and pick up an AMCAS med school admissions guide so you can see and review just what each school requires.
There are plenty of undergrad research opportunities at UNC, you just have to look for them. There have been several posters on CC in the past who either were freshmen doing research or their parents.
You'll get actual AP credit for the course as if you have taken them at UNC and unless I am wrong, Duke only gives course advancement. For med school that would mean having to take more upper division Bio and Chem classes than required if at Duke; why do that?
My S graduated from UNC in May. He is currently an MS 1 at a top ten med school. He entered UNC with 43 AP credits which allowed him to by pass intro level Bio and Chem (among others) which notoriously at most schools tend to be huge weed-out classes with very strict grading curves. It also allowed him to be in all upper division classes by second semester freshman year which kept his class sizes and exposure to TAs down. In his circle of friends, three others are now in med school with one at Harvard, one at Georgetown and one at UNC (she was an in-state Med School double legacy).
Duke may have an edge in formal pre med advising and I believe also has advisers who write letters of recommendation as part of their advising program which UNC does not have. That said, I still think UNC can prepare you well for any med school.
Unless you are a Hispanic from a prep school background and very wealthy family I think you will find the fit at UNC to be more to your liking.
Don't forget the cost differential;my S turned down Yale to attend UNC on a merit scholarship and graduate debt free. Med school is very expensive and it is a LONG time before you make any money of consequence.