I found an excellent article that actually did research into the best way to do drop down menus.
Here is a link to the article: Best UX Pattern for a Website Navigation With Dropdown Menus
- Hover-to-open drop down menus are easier for users than click-to-open menus.
- If the top-level page had unique content, you should include it in the sub-menu as well. For example Services > All Services. But if the page is simply a landing page that links to the other pages it’s probably not necessary.
- Making the top menu also clickable is generally a good idea.