I would go with the second option because it allows you more flexibility as you don't depend on traversing the hierarchy using the same route each time. I'm assuming that Style, Article and Size are independent from each other and you can have the same size within different articles and styles. Using a hierarchy, each instance of size will be different and it will create more problems when you try to get a report by size.

This is unless the 3 dimensions are small enough for a junk dimension to make sense.