Ok, so I've been doing some more thinking and talked with some American friends about your choice. Here's my thoughts...
Both universities have similar reputations in US. Duke is bigger and know better outside of US.
Both universities are known to be fun. Emory has the city and there's a lot of partying in Atlanta. Average age in Atlanta is about 31.
The difference in salaries is probably due to management salaries being higher than marketing salaries.
Having a scholarship plus MBA will look even better on your resume.
One of the main reasons for doing an MBA is to build lasting relationships with people that will be influencial in business and can help you succeed in the future. Both universities will give you this.
My friends, and I tend to agree, that its not worth the extra money for Duke. Plus Emory ranks better for what you want to do!