Need your advice. MultiSite
Given your description, the domain access module is the better way to go. Drupal multisites won't give you the capacity to have one main site and many smaller sub sites but that is the key feature of domain access:


  The Domain Access project is a suite of modules that provide tools for
  running a group of affiliated sites from one Drupal installation and a
  single shared database. The module allows you to share users, content,
  and configurations across a group of sites ...