Well, basically it depends on where are you going to use the language. BrE has a clearer pronunciation and they speak more formally really often. Instead, AmE is more relaxed and it's a little easier to understand, well, at least for me.
Here, in Argentina, where I live. We learn British English in school, but sometimes they give us a few skills to understand other accents. There are some places where you can learn American accent if you are interested in.
I haven't get into medical school yet but I would choose the most appropiate accent especially the one the meadical treatments comes written in.