Search for. choose the topic that will be the most
personal, detailed, honest and
revealing about you.
If that topic is not the transfer, but you feel the need to discuss the transfer beyond what your GC would say, then consider discussing the transfer in a supplemental essay.
Don't worry about whether other people have written on your topic. One of the best and most memorable essays I've read, and I've read hundreds, was on that very topic, "why I want to be a writer".
Your take, your experience can be unique in all history.
It is a great mistake imo to search for that topic, say, gecko racing in Antarctica, that no one else has ever heard of.
It's not the topic, it's what you do with the topic.
For good advice on essays, see
U.Va. Office of Admission Essays