The schools you apply to depend upon a variety of factors, including:
-what your chances for admission are
-what region of the world you'd like to work in and/or study in
-what your post-MBA career goals are
-what size of class, curriculum, teaching style, etc you are interested in
-length of program
-any other specifics you are looking for
In terms of the first point about your chances for admission, you can look first of all at the average GMAT score of the schools you are interested in, and ideally you want to be close to the average, or above, at schools you apply to. For US schools with a 680 you'll generally be looking at schools ranked 10-20 or so. But there are so many factors to consider when choosing schools, it is worth doing some more research to determine what you are looking for.
Good luck to you.
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