In the USA there are two major divisions in most dancesport competitions: American Style (Smooth and Rhythm) and International Style (Standard and Latin). If you think you are going to continue to go back and forth between the US and Europe, then the best thing to do is to learn International Style.
I am not sure what you mean by English style, unless you mean English Sequence Dancing. If you like it and will be living in England, then it makes sense to learn it. Australia has something sort of similar, called New Vogue, but I don't really know much about it either so I'll stop here, other than to say that in England there are Sequence Dance competitions and in Australia there are New Vogue competitions.
In the US, popularity of American Style versus International Style at competitions does vary by region. Apparantly American Style is much more popular in the central part of the US, and International Style on the Coasts.
Again, if you want to pick the one dancesport style that will be the most portable no matter where you go -- even to Asia -- then go with the International Style.
