Stanford or Harvard

if financial aid is something you're concerned about, then the answer is Harvard. Harvard is need-blind for international students, while Stanford is not. beyond that, you're basically choosing between two of the best five or so colleges in the US—they'd both be phenomenal, and there really aren't substantial academic differences between the two (location is the only real difference). Harvard would just be significantly easier for you to get into if you plan on applying for financial aid, so I'd use your REA boost on them.

for your other question, getting rejected applying REA is basically the same as getting rejected for RD—in one case you get rejected in December and in the other you get rejected in March. you used up your shot on that school. but REA gives you a slightly better chance of getting in and there's no risk involved—and if you're a strong applicant, they'll usually defer you instead of rejecting you in REA, which means you'll be considered for RD anyway. sorry if that's confusing, i guess comment if you want me to clarify anything!

editing to respond to your comments:

the truth about schools like these is that, in the end, they are going to give you very similar opportunities. the choice between Harvard and Stanford is like choosing which five-start restaurant you want to go to for a meal. both of them are going to be excellent, and neither is a bad choice, but maybe one serves food that's more interesting to you than the other. if you're worried about admissions, they're both difficult to get into, but Stanford is actually more selective than Harvard is (by a small margin). if you're an international student applying for financial aid, Stanford will be significantly harder to get into than Harvard, because that will affect the decision there (it won't at Harvard, because they're need blind). of course your chances of getting in are going to depend on your grades, SATs, etc., but the fact of the matter is that in your specific situation, stanford will be harder to get into.

with the other places you mentioned, Princeton would actually be another good choice that is need-blind for international students, so you would have a better chance of getting in there than you would at Stanford. UC Berkeley is a great school but they barely give any money to anyone who doesn't live in California, so unless you're okay with paying $70k/yr to go there, it might not be the best choice. in reality though, there's very little to separate any of these schools. they're all very similar academically, would give you similar resources and similar access to professors, would allow you to pursue research, etc. i'm focusing on financial aid because that's the only real significant difference between them.