@rustykenSome of this comes down to what the story is. If it's one story, self-contained (and however long), and posted all at once, my preference is end notes (likely along with a pointer to it in the Foreword).
However, once you go to serialized posting, that becomes cumbersome and annoying. In that case, 'at the beginning' becomes fairly reasonable. The big 'gotcha' is that a cast list can easily become a huge bundle of spoilers, and - if it's at the start - it's in exactly the wrong place to avoid actually becoming spoilers. New readers need to actively avoid the cast list.
For a multiple-story work, I would strongly suggest a cast list at the end of each story. Thus, the Book 1 cast list, at the end of Book 1, contains spoilers for Book 1, but that's fine. Anyone reading Book 2 can refer back to Book 1's cast list. Changes to characters within Book 2 won't be covered in a cast list until Book 2 completes posting.
If it's necessary to have an 'interim' cast list, it should be posted as a separate 'story' and deleted when a story is completed.
I've been 'working on' cast lists for a long time, but I'm not there yet. So, I have opinions, but not a working model to point to :)