Yes, there are differences between the two styles, but there are some similarities, too. As for which to learn, it's mostly a matter of preference, I think. But it can also depend on the crowd in your area. For example, if most people dance American at social dances, you'd probably want to learn that rather than international. At the college I went to for grad school, we usually gave newcomers this advice: start with American style and then try international later unless you plan to do most of your dancing outside of the US, then do international from the start. The idea is that in the US there is (or was) this idea that American style is for social dancing and international style is for competing. So when it's taught, at least with our club classes, the American style classes are a tad more relaxed than the international ones. You'd get good technique and such in both, but that would be stressed more in international than American and when you're trying to draw and keep newcomers, you don't really want to put them off with too much detail. I think I'd say look at the crowds of people you want to dance with, and learn the style that most of them do. That way it should be easier to dance with more people. I hope this helps.
