How To Manage a Webform and a Contribution page?
As far as Civi and the payment processor are concerned, both methods are the same. It's the same contribution page, just presented 2 ways (full-screen, or embedded in a drupal webform). So it just comes down to your preference about the user experience. The first option would present fewer screens to the user, since the 2nd option involves 1 page of webform + 2 pages of contribution form.