What’s the difference between clipping to these three formats? What are the pros and cons of each, and also which one is more suitable for long-term, offline storage (so that images and relevant data is downloaded)?
Resource is the item as is, typically a HTML file.
Web archive is intended to be an offline archive of the page though it’s not as useful as it once was due to the way content is delivered on many sites nowadays.
Formatted Note is an HTML page with the content of the page captured. The styling isn’t necessarily captured and there is still the possibility of content not being captured.