42,000 per year Northeastern American is 45,000 per year not a big difference, but I would try and negotiate a little scholarship money from each school. Both Boston and D.C. are expensive areas so again not a major factor, but if you have family and friends in Boston they may be abel to help you if you stick around the area. Just somethign to consider, but this looks like a draw. 3. Personal Feelings about the School
Each law school has a culture to it some you will like others you will not. As a 0L I visited multiple schools and while in law school I participated in multiple mock trial competitions and there really is a culture to each school. One thing I noticed is that American seems to have 3x as many law students as NorthEastern so will you like a larger more anonymous school or a smaller environment? Again neither is right or wrong it is just what suits you best. I personally liked the smaller schools, but that is me.
What I would recommend is visiting both schools, talking to professors, students, looking at the campus, and listening to your gut about which one feels right. I know I visited some schools and said no way and others I loved. It is personally possibly you will like the schools I hated and hate the schools I liked nothing wrong with it, but it is 3 years of your life, 100k of your money, and your legal career so take the time to visit the campuses and see what feels right. 4. Reality of Legal Education
It is all the same, which is why you shouldn't take U.S. News Rankings to seriously whether you attend Harvard or Cooley they are all subject to ABA regulations and your first will consist of Torts, Contracts, Property, Civil Procedure, and Criminal Law/Con Law/or Crim Pro in year 1 and the others in Year 2. In these courses you will read Supreme Court Cases and believe it or not they don't write sepearte opinions for different ranked law schools. In Torts you will read Palsgraf to learn Proximate Cause whether you attend American or Northeastern, Pennoyer v. Neff to learn Notice in Civ Pro, International Shoe for personal jurisdiction, so on and so on.
At the end of your three years you will then have to take a State Bar Exam and you will sign up for BarBri or Kaplan and be in classroom with law students from around the County after months of intense studying you will go into a room with Thousands of people and take the exam. If you pass your a lawyer if you don't your not and the bar graders don't know or care what law school you went to. Once you have a license to practice law it is then up to you what you do with it. (5) U.S. News Rankings
You mentioned this in your post and I can't tell you how many 0L's myself included when I was your in shoes take this magazine way to seriously. Remember it is just a magazine and the methodology used to make the rankings makes little to no sense. There are some schools that have true prestige Harvard, Yale, Georgetown, etc, but nobody cares about the difference between American and NorthEastern I don't know what they are, but I am guessing these schools are somewhere between 50-150 and I can't remember the last time I cared about the 50th best anything.
Also remember U.S. News ranks a lot more than law schools Alberque is the best place to live according to U.S. News cite provided http://money.usnews.com/money/personal-finance/slideshows/best-places-to-live
. Our Balloon Festivals, Clear Skies, etc good things sure, but I don't think your going to pack your bags to move based on what U.S. News thinks. The same logic applies to law school don't make a life altering decision based on a magazine. I imagine you would think it was crazy if someone moved to New Mexico based on that ranking the same is true of law schools, but for whatever reason 0L's get enamored by a magazine, but that is all it is a magainze. You should use it as a tiebreaker not a primary source of your decision.
Additoinally the rankings change year to year based on god knows what as you can see from this chart American has been as low as 56 and as high as 45 additionally there are an exorbiant number of ties 2 years ago there was a 13 way tie for 84th, which was pretty good. Northeastern has been as high as the 70's and as low as the 90's it is very possible by the time you graduate NorthEastern could surpass American it is all based on people filling out scantrons. So again don't make a life altering decision based on the rankings particularly with schools of this caliber. If you were debating Georgetown over Northeastern then rankings might play a factor, but nobody cares about the ranking difference between these two schools.
There is no right or wrong answer it is up to you to analyze your unique situation. I have never set foot on either campus, but you will receive a solid education at any ABA school.
Also one other point of caution you mention transfering, but this is not something to bank on. The reality is you need to finish in the top 10-20% to transfer and everyone at an ABA law school is smart, hard-working, and motivated meaning there is 80-90% chance you will not finish in the top 10-20%. Nothing against you just the way it works you will see on the first day of class when everyone is convicned they will be in the top 10% and nobody could possibly imagine finishing in the bottom half of the class, but it happens. Bottom line don't attend a law school you won't be graduating from transfering is extremly rare so don't move to D.C. certain you will be able to transfer back for 2L to Harvard or something it is highly unlikely to happen.
Good luck and congrats on your acceptances.