Best approach for [back][next] form submitting
You should always use the Form API for forms, unless you really wanted to use the Webform module. The learning curve it steeper but you gain more maintainability (everything is in code from the start) and flexibility. You can create multisteps form with the API. See form_example_wizard.inc and Drupal 7 multistep forms using variable functions (also with Drupal 6) for examples. Another solution, is to use the CTools' wizard API.