Hello Rodger,
Deciding which editor to use is largely going to be a matter of personal preference. The best analogies to think of is that the Classic Editor is most similar to a classical Word Processor, the WordPress “Gutenberg” editor is a creative writing tool, and the BoldGrid Post and Page Builder is more like a graphic design tool.
Of course, all of the editors can be used for word processing, writing, and design, but each have their strengths. For example, many BoldGrid users prefer to use the Post and Page Builder for their main marketing pages, while using the WordPress editor for their blog writing. I hope this helps!