Should I use Drupal fields or tokens?

It depends on the use case. For fields and their field formatters use a 'Field' element, for data without field formatters, use a token.

There is no right or wrong answer to this question, as it depends on the use case. 

If you would like to render your field data with your Drupal field formatter, then use the Site Studio 'Field' element. If you would like to render the data, use a token. 

Drupal tokens allow you to pull field data through into a Site Studio element without the Drupal field formatters.