when someone says "waltz" with no other qualifier, my assumption is that I am doing a slow waltz...as in American or International (have never had anyone use the term English or Boston)....having said that, I am aware of the many other types of waltzing that exist
Today, with no other qualifier, I would think slow waltz. Before I started dancing and knew the difference, "waltz" was a mixture of slow waltz and Viennese Waltz. Though I agree with DOI - from a music perspective, I'd go with the time signature answer.
In Vietnam, we play Quick & Slow Waltz. Slow Waltz have two styles: French Valse Boston (Cross-step waltz) and English Waltz. Boston was popular several years ago, when dancesport not well-known, and often used for beginner or female who doesn't like closed frame.
Like others, music is the most important, but if I have to choose, English Waltz is my favour.