beautifullife

I can speak for Canadian schools. You have low chance. 

LSE is excellent if you are thinking of applying to PhD and if the costs are not main concern. They have a good track record of placing their graduates in good PhD programs. Also, their masters degree includes conditional offer for their MRes/PhD which is a bonus, since you don't have to worry that much. LSE is definitely a good option for PhD too. Further, LSE has a stronger theory group than the other schools, see John Hardman Moore.
In Europe PSE masters program does not have as strong reputation, especially in Micro. This might be different in US, though. Also, free tuition is great. £40k+ of debt after a year at LSE is not appealing for me.

I was applying to UofT this year as a backup and I can tell you that they are willing to increase you financial package if you want to negotiate. They more then doubled mine to $40k+ (including TAship) when I indicated that I might still consider their offer.
Finally, remember that the admissions to PhDs at Top 10 are much more competitive then to any masters program. No matter where you end up going, make sure that you are at the very top end of the distribution so that your reference letters will shine. 

Rescinding is not an option, it's something you have to go out of your way to find and do. That's why it's frowned upon.

Well said, Tams! I'm in a similar boat as the OP. I only applied to schools that I would be happy going to.

I've accepted an offer from Penn for a Master's program because the deadline was April 15th and it made financial sense to commit. However, because GWU is my first choice and they have a June 1st deadline, I'm going to continue applying for jobs with GWU to get tuition remission. I know that is unfortunate for Penn, but if they offered me more money, this would be a no brainer. If GWU comes through with a job for me, then I'm off to GWU. You have to do what makes sense for yourself, because after all, this is YOUR degree, YOUR time, YOUR money.

If it's unethical to take up someone else's spot, then why even apply to more than one school if you can only choose one? Wouldn't you be taking another applicant's spot if you weren't completely head-over-heels committed to the school? You can argue that by applying to six schools and being admitted to all six (like I did), and I obviously cannot go to all six, I was taking up a precious spot on the admitted students roster. That's what waitlists are for. Schools are used to admitted students dropping out. You have no reason whatsoever to feel guilty. If anything, you should feel guilty for attending a school you weren't excited about because you felt too guilty to drop out and attend your dream school.

Good luck!

Why is it a bad idea? Because it's unethical. That's why.

When you accept an offer, it is expected that you will keep your word. You do not want to burn bridges by actively screwing schools over.

Of course, everyone should apply only to programs they absolutely want to get into, but obviously not everyone knows the circumstances under which they will get in (i.e. funding, housing, status, etc.) Trust me, I understand the difference in timelines, as I applied to both Canadian and U.S. schools. I could go on about the points made here, but I am just too flustered at a couple of the replies...

HisRoyalHighness, math123, you HAVE to be kidding with that rhetoric. "shocking", "disgusting", "amoral people"? Did you ever learn the difference between a healthy debate and personal attacks and judgment? Please spare us your exaggerated self-righteous remarks. 2400 actually sought honest opinions because he/she is in a very agonizing predicament. I don't know if you have found yourselves in that situation before, but regardless, you have no right coming in here and pouncing on people with such unnecessary attacks. "SHAME" on you. Ignorant voices are indeed always shrillest.

By the way, for your information (not that you seem to care about that much, since your morals are so high and mighty), programs usually account for students rescinding their offers, as this happens every year for a variety of reasons, foreseen or not. They were not born yesterday. They caution you against doing so for the purposes of their administrative processes, as it is a pain for them to close the file of a student whose status was accepted/gave intent. Especially for MA programs, professors are usually not even aware of who came and went, and bitter feelings and bad reputations are unlikely to result. This is particularly true if you give a reasonable explanation. Yes, I did ask two reliable sources in academia about this. Don't worry, though, you can still keep your world black and white the way you like it.

2400, best of luck to you and I am truly sorry you are in this situation. That's just how it works, I guess...they dictate your application deadline and your decision deadline...and many deadlines to come Please do try to get an extension though.

And please, people, can we act like potential/current grad students and stop the counterproductive insults?

I see where you are coming from. I totally acknowledge that Duke is a decent school. It can be compared to some of top Canadian schools like U of Toronto, which also regularly ranks within top 20 in most fields. That being said, I don't really like to distinguish schools by rankings but considering European and Asian schools, both Duke and UofT don't really place within top 20 in the world anymore in a lot of fields. They do in any respectable American sources that ranks based on English publications and citations made in English journals. Then, there are Princeton, Harvard, Yale, Columbia, and several others. There are some traditional American schools that just won't be defeated by anyone's, any rankings, and any places. 
Ask any professor in Government field. They will tell you Princeton is a better school. Also, the post was made by someone who is applying to government studies, which is a field quite clearly Princeton does a better job at placing their graduates. 

I'm not sure where you're pulling your information from but: Princeton and Duke are both well-regarded schools. Both schools are "regarded" as top 20 programs in multiple fields. Princeton is in the Ivy League but one has to remember that the Ivy League is a sports conference. It doesn't mean that schools that aren't in it don't offer "better" academics. There are a lot of great schools comparable to Princeton and Duke.

I see where you are coming from. I totally acknowledge that Duke is a decent school. It can be compared to some of top Canadian schools like U of Toronto, which also regularly ranks within top 20 in most fields. That being said, I don't really like to distinguish schools by rankings but considering European and Asian schools, both Duke and UofT don't really place within top 20 in the world anymore in a lot of fields. They do in any respectable American sources that ranks based on English publications and citations made in English journals. Then, there are Princeton, Harvard, Yale, Columbia, and several others. There are some traditional American schools that just won't be defeated by anyone's, any rankings, and any places. 
Ask any professor in Government field. They will tell you Princeton is a better school. Also, the post was made by someone who is applying to government studies, which is a field quite clearly Princeton does a better job at placing their graduates. 

I think @QK91 summed it up pretty well.  And from reading between the lines it looks like you're leaning toward Princeton on points 2 and 3.  I would actually go further than QK on both points, because it's my impression that Princeton is one of the 3 or 4 globally recognized U.S. universities, whereas you can't say the same about Duke.  
Also, for point 3, I heartily agree with your suspicion that the Princeton area -- an hour or so from NYC -- is way more interesting for an international student.  That's where I'd want to be if I were coming to the U.S. for the first time.  Don't get me wrong -- I've lived near Durham for 15 years now and I like the area.  It's only 20 minutes from Raleigh too, which is a cool, up-and-coming mid-size city.  But it's no NYC.
So unless you see something about the Core or other course offerings at Sanford that really sways you, it seems like Princeton is a better fit.  I say this reluctantly because I too am going to Sanford and would love to have another highly-competent international student in my cohort. . . but the good news it that you can't really go wrong when choosing between two amazing places, so congratulations on that at least!