We have had multiple family members attend both Harvard and Tufts.
Tufts has a unique culture that is quite different from the Ivies. If that culture resonates with you, then you will not find a better school.
Based in what you said, is not even a question. Go to Tufts.
OTOH, please make a trip to the Harvard Club on Commonwealth Avenue in Boston, and observe the iridescent chandeliers illuminating the well-dressed men and women being served by waiters wearing white blazers, sipping champagne and other fine wines, and smiling with the quiet satisfaction of having entered into the world of elites only a Harvard undergraduate degree can confer. Then ask yourself whether you can give up this unique opportunity…
OTOH,
MIT alums can also join the Harvard Club (if they are interested) and if you want to live that lifestyle outside the confines of the club, a Harvard grad is probably going to have to borrow money from his/her less ostentatious MIT and Tufts friends, because it is likely that they will be making more money and spending less. 
This is despite the fact that Tufts has a much higher percentage of art majors, a lower percentage of STEM graduates and sends a much higher percentage into the Peace Corps than either Harvard or MIT.
http://www.payscale.com/college-salary-report/best-schools-by-type/bachelors/research-universities
payscale.com/career-news/2014/09/introducing-the-2014-2015-payscale-college-salary-report
Just a note, the salary data you posted on another thread is circa 2008, when the Payscale database was smaller, and there was not enough sample data to include Tufts…
I’ll admit I didn’t read this whole thread, but I’ll just add my two cents.
I’m an undergraduate student who works with a PhD candidate in a top 3 program in his field in the country. He was accepted to Harvard for undergrad but decided to go to another school instead because it was a better fit. You were accepted to Harvard because you are obviously a very, very smart person with a bright future ahead of you. No matter where you go, you will be fine.
I personally say go where you think you’ll be the happiest. Four years is a long time to be at a place about which you’re unsure.
Good luck with whatever you decide 
If the cost is the same, go to Harvard.
I must say I am surprised no one is sticking up for Harvard’s econ dept. And there must be someone that feels that you can find a “warm + welcoming community” somewhere at Harvard.
My daughter is trying to decide whether to decide whether to stay on the Harvard wait list because she doesn’t want to have to make this decision (vs Tufts) if she were lucky enough to get in. I was hoping to hear some kind of argument other than the opportunities/prestige one.
But only 41 Tufts alumni responded to the payscale survey, including four dentists who reported an average salary of over $250k, so I don’t believe the survey is statistically relevant, unless I’m missing something.
Most people are making the argument for Tufts based on the OP’s original statements about perceived “fit,” which I think is a very valid way to think about the decision. I don’t think it is a matter of “sticking up for Harvard’s econ. dept.” which is of course excellent. For undergraduate work, the OP will be in excellent hands at either institution. But I have to admit that the elitism/prestige argument–especially when framed in terms of sipping champagne and wearing white jackets at the Harvard Club–would completely put me off and make me choose Tufts. (And this is coming from someone who attended “elite” institutions for both undergrad and grad school). So I’m in the “if you are good enough to get accepted to Harvard, you’ll do great work and have a promising future wherever you go” camp. I think that may mean a vote for “fit” at Tufts, if that is where the OP’s heart lies.
What @profparent said. Prestige is all very well and fine, but it isn’t everything, and can frankly be off-putting for some. A little goes a long way… Follow your heart.
Part of this is in jest, but what if the OP wants to be the POTUS or a U.S. Senator? Harvard will open many, many more doors than simply the keys to the Harvard Club on Comm Ave.
I have a friend who graduated from Harvard many years ago and this is his perspective: When you get accepted to Harvard, you are brought to a set of beautiful double doors. After being given a minute to admire the doors, they are opened. Inside is every educational opportunity that can be imagined. No expense spared. Both broad and deep. There is no better combination of opportunities anywhere. After admiring the opportunities for a short time, you are pushed in. The doors are closed. No one is around to help. Some people thrive and make use of the opportunities. Others, wish they had a little more “hand holding” and also wish they had not gone through the double doors.
I’m guessing that if OP wants to be POTUS he a) already knows that and b) would be choosing Harvard without our help. Most of us don’t (want to be POTUS).
@profparent I totally understand the broader “fit” argument, but for IR and Econ, Harvard is probably top 5 for both, so I would think it would be hard to pass up. I have no problem with anyone choosing Tufts over Harvard, I’m just a little surprised the debate is so one sided.
I understand your point, ormdad, and of course you are right about the rankings, but because the OP listed IR as a definite “plan” and Economics as just a “possibility” and because she mentioned IR twice in the original post, I focused more on the comparative IR programs, and Tufts is, I believe, in the top 10-20. (Harvard is definitely above that, but I don’t happen to believe that for undergraduate work the comparative rankings in the top 20 schools are as important. For grad school it would be a TOTALLY different answer–definitely Harvard). Now if the OP were truly serious about an Economics major, then I might change my advice–at least to note how much stronger Harvard is in that field. But students so often change their majors, and the OP was so very clear about feeling uncomfortable with Harvard and feeling that Tufts was a perfect fit that I would have a hard time arguing she should choose Harvard based on the comparative excellence of a department she has only expressed a secondary interest in.
Agreed @profparent. I am just a little surprised that the Harvard bandwagon never showed up.
Tufts vs William and Mary for IR, or Tufts vs WashU, or even Tufts vs Michigan gets a much livelier debate on these forums.
FWIW, this undergraduate ranking of IR programs shows Harvard at #1:
http://en.wikipedia.org/wiki/Inside_the_Ivory_Tower
Tufts is indeed in the teens, which is certainly respectable. Fletcher is #6.
A lot of the thread has been devoted to fit. For me this is more significant when comparing an urban university to, say, a rural, exclusively undergraduate-focused LAC. I could see how a student could only be happy at one or the other.
Regarding Tufts and Harvard, I think the comparison is a straighter one. The Harvard advocates, though they came in later, did make some substantive points regarding Harvard’s considerable academic strengths. Ultimately, evaluating the two universities along these lines seems to make sense. Fit may be a sub-factor.
Btw, does anyone buy that the Payscale stuff is scientific (self-reported and tiny samples)? Beyond that, money alone may not be the goal for many students.
Thank you all for your input.
Proud to be a part of the Tufts c/o 2019!
Congratulations!