Different styling for each teaser display
You can create different Entity View modes instead of the single teaser. While you can do that via a custom module in Drupal 7, there is a nice little module for that (https://www.drupal.org/project/entity_view_mode) too.

Create different modes like 'teaser_front', 'teaser_sidebar' and theme them differently using the standard theming convention (can also be found in the module page).