The locations will sell some Disney treats, like specialty cupcakes. For instance, you can buy the BB8 or Chewbacca cupcake at the Starbucks in Hollywood Studios. So that might be an option, especially if you like your Starbucks drink but want a Disney treat.
I've visited all the Starbucks locations at WDW (and DLR...I may have a problem). The best WDW Starbucks, IMO, is the one found at Disney Springs West Side. Inside the four parks, I'd probably choose DAK because of its outdoor seating. (And maybe the Zebra or Cotton Top Tamarin Cupcake.)