Which one do you need?

The two tools differ in one respect: how much of the page ends up in the image. That sounds trivial, but it decides which questions the screenshot can answer.

Choose the viewport screenshot when the question is about first impressions — what appears above the fold at a given width, whether the call to action is visible on a phone, how much of the page a consent banner covers. Fixing the viewport is what makes the answer meaningful.

Choose the full-page screenshot when you need the complete document — a terms page, a long product listing, an article — especially if you will refer back to it later as a record of what was published.

Both are one-off captures. If you find yourself taking the same screenshot repeatedly, that is a schedule waiting to happen: an account lets you capture the same page automatically and deliver every result to Google Drive, Dropbox or S3.

Automate the captures you keep repeating

Set a frequency and a timezone once, then let the history build itself.