Switching research topics to something less interesting? I'm finishing my undergraduate degree this year, and I'm deciding which PhD program to attend: School A, or School B. I do have other offers, but these two stand out to me. My background and current interests are in topic X.


School A has exactly one professor working on X, but my would-be initial advisor works on topic Y. I don't oppose doing research in Y, but my background and current research interest really is X. This initial advisor is recruiting me very aggressively, so it'll really hurt turning him down.
School B has 2-3 professors working on X, but I can't see myself working with anyone here whose research is not in X, which would be bad if I lose interest in X someday. If the would-be initial advisor at School A weren't recruiting me so aggressively, I'd choose School B.


All of the aforementioned professors are quite productive, though the students at School A are slightly more productive than those at School B. If it matters at all, I prefer the location of School A slghtly.

tl;dr: School A is aggressively recruiting me and may be the better place overall, but for my current research interests, School B is the place to be.
If you want to do research on X, you should go to a place where you can do that! Going to school A, working on Y, and hoping that you might be able to switch advisors does not sound like a good idea. How much the professor at school A wants you should not really matter, you have to do what is right for you; he will find someone else. Moreover, I would not already think about what to do if I lose interest in X. This is hypothetical anyway, and in this case, there might be some topic Z that is more interesting than Y etc.