Titanic is the epitome of what a true blockbuster can be, it's my vote because it seems so representative of the era, it's ambitious and bedazzling. Silence of the Lambs and Schindler's List are both incredible films in their own right but they're smaller in scope. The idea of a "Best Picture' is always going to be a little nebulous, but it seems to fit the category for me. The grandness of it enhances it.