What are the Drupal modules most used with CiviCRM?
I am quite curious about why you are asking this question. My advice would be to install only modules when you have functional need and those modules solve them for you.

It might be even that a module which is used often is completely useless in your context. Or that it breaks other needed functionality. 

Having said that the masquerade module is very handy one. Same as views and webforms.