I am working part time at Taco Bell right now for some extra cash. I can assure you that the drive through gets the priority. All of these fast food places keep metrics on how long a car sits at the screen ordering and then how long they spend at the window paying, getting their food and driving off. It's projected on a screen in the service area and averages throughout the entire day. Corporate watches this. Drive through orders are ALWAYS prioritized.....so you wont get better or faster service by parking and going inside.I go on Sunday because the lines are much shorter.
Actually I don't like drive through anything, so I just do inside. The lines are much shorter, the people at the counter are friendly, and the food comes to my table quickly.
As to Whataburger, my daughter's boyfriend is a life long Texan and says that since they were bought out the quality of the food is not nearly as good as it used to be. I've only eaten there a couple of times, so at the risk of being asked to leave the state I'll just say that I don't think that their burgers are anything special.