JerBru,
As Scott said they are two different programs. Some people use both, some use VSD, and others use the HTML Editor. The two programs VSD and HTML Editor have very different interfaces, and of course the HTML Editor has two different interfaces. My preference is the HTML Editor in the code editor mode. I seldom use the visual editor in HTML Editor, and use VSD just to see what it can do. Some that use the visual editor in HTML Editor will occasionally make minor edits using the code editor.
If you haven't used all the features of HTML Editor, you are right in step with many others of us. I just found a feature in HTML Editor today that I has not noticed in the past. So play around with the various tools and sections of HTML Editor and see what they will do. I do suggest you setup a test section for those files and not use the files that are actually on your site.
If you have not tried VSD, check out the trial version and see what it will do. You may find that it has an interface that suits you, or you may find that you prefer the visual editor in HTML Editor.
If you have any questions about the programs, ask here. It is likely that someone will have an idea how to do what you want done.
As it happens, your questions caused Jim to create a set of instructions on how to use bookmarks with VSD. So ask away. I enjoy learning something about HTML every day on this forum.