@vnszzz I’m obviously biased because I’m going to Brown this year, and applied ED (deferred and accepted RD,) but COME TO BROWN! 
However, I do know a student who was admitted (and is attending) Duke ED last year.
First things first, Brown and Duke are VERY different schools.
Brown’s Open Curriculum is PERFECT for students who are interested in delving deep into 1-2 interests, but don’t want to give up other passions (virtually no requirements, except for 2 writing designated courses, which are offered in a variety of fields.) This also makes it extremely easy to double-concentrate if desired, and ~20% of undergraduates do!
There are more student-friendly grading policies here than at Duke. You’re able to S/NC (Pass/Fail,) any course, which is great for electives (like language courses,) that you’re interested in taking but don’t want the fear of getting a bad grade stopping you. There are no +/- grades, and intro STEM courses are not curved, unlike some other schools (like USC.) You can drop a course the day before the final exam period starts, and failing grades are NOT recorded on your external transcript (i.e. the lowest grade that could be listed on your external transcript is a C.) Brown also has a shopping period (similar to Yale’s,) where you can sample multiple classes for the first few weeks of the semester before deciding on which to take.
Brown has a strong graduate program acceptance rate (90%+.) Both schools have alumni/ school sponsored internships, but the specifics vary. Also, they both allow you to create your own major (or concentration at Brown) through Brown’s Independent Concentration program and Duke’s Program II Major.
Durham is far, far, far warmer than Providence (which is basically Boston in-terms of weather,) so keep that in mind when deciding. You’re not just attending the school, but you’ll be living in the city as well for the next four years.
Brown doesn’t have a major emphasis on sports unlike Duke, where sports (especially basketball) are a HUGE part of school spirit.
Duke has a distribution-based general education requirement system (although with more freedom at Pratt vs. Trinity,) so keep this in mind when considering the feasibility of double majoring, exploring electives, grading policies (+/- exists here, and there is a lack of grade inflation) etc.
Financial-aid wise, both schools meet 100% of your demonstrated need. HOWEVER, Brown (under the Brown Promise,) DOES NOT include loans in aid packages, whereas Duke DOES for some students (the amount depends on your parents’ income.)
Brown FA: financialaid.brown.edu
Duke FA: https://financialaid.duke.edu/awarding-and-policy
While both schools have similar undergraduate class sizes, Duke has ~5000 more graduate/professional students than Brown. At Brown, there are 1/3 the amount of graduate/professional students than the amount of undergraduate students: this means it would be easier to conduct research and other opportunities with professors, as there is a smaller graduate/professional student population present.
Duke’s Admissions website makes it clear that applying ED DOES have a benefit, whereas Brown’s Admissions website states that ED applicants are only admitted if they would have been admitted RD as well. However, this is not entirely true, as applying ED is the ULTIMATE form of demonstrated interest (even at the Ivies, who don’t consider it on paper,) and if your application can SHOW, NOT TELL (as @lookingforward said) your fit for the school, you will have a higher chance of admission than the applicant applying right before the deadline. Furthermore, for this year in particular, multiple students from my schools applying to Ivies were deferred ED and accepted RD (and at Brown from watching YouTube Decision Reaction videos.) I was admitted RD to Brown despite another student having been admitted ED, so it is possible to still be admitted even if deferred, so make sure to look-up what a Letter of Continued Interest is for deferred/wait listed applicants if that ends up being the case (but fingers crossed you get in ED!)
After further research if Brown or Duke is your top choice, I highly recommend you apply ED, but ONLY if ALL of the following is true:
- You LOVE Brown or Duke and would 110% attend if admitted.
- You're confident you can present a well thought out and crafted application by the ED Deadline, which is November 1st.
- You and your family can afford Brown or Duke if admitted (run the FA calculators if applicable.) Although Duke DOES offer merit scholarships, these are HIGHLY COMPETITIVE and the receipt of one should be considered as nothing but a pleasant surprise. If you and your family would REQUIRE one of these in-order to attend, it would be better for you to apply RD to compare scholarship offers between colleges.
Hope that helps and good luck with admissions! Let me know if you have any other questions about why I chose Brown, or about the admissions process at Brown in-general!