How to have a drop down table populate based on another field selection

You need to add a link to it in your html file, something like

<script src="../jquery-1.11.1.js"></script>

obviously substituting the correct name and path.

I’m not sure there’s a definitive “better” - your browser will probably cache it once it’s been referenced the first time anyway, so download times only play a part the first time. If you host it, you can be sure that it will never change, but then I think if you reference it on the hosting site older versions aren’t changed or removed.

You could also have a look through this very similar post, which isn’t quite the same, but could be easily modified to do what you want: Filter Dropdown menu item by value