You definitely want Slow Waltz at this stage. It's not that Viennese is necessarily out of your reach, but you're going to get that nice graceful feeling much sooner in Slow Waltz than if you pursue Viennese. Also, Slow Waltz is a good foundation for Viennese, so you'll be doing things in the right order.

As to whether you choose Int'l or American style, that's probably going to be a more subtle distinction, since there's so much overlap between the two (particularly in the Waltz). You can't really go wrong either way. American style might provide a more instant gratification, but that really depends on the teacher. If you see yourself doing open figures like underarm turns and the like, you'll want to go with American style, since Int'l style never leaves closed position.

Regards,
Jonathan Atkinson
www.ballroomdancers.com