South America backpacking: 4 week route for a first timer?

[TravelNotes]

I would include Colombia as well.

Colombia: Medellin or Cartagena for a first timer?

I only have 6 days to visit Colombia and I know I can’t do both justice. I love history, walking around colorful streets, and good coffee. Cartagena looks gorgeous but I’ve heard the street vendors are super aggressive. Medellin looks incredible but maybe less “vacation-y”? Which one is better for a first time visit?

Michel.