If you’re buying a new car you won’t have much of a choice. These days I’d skip the extended warranty. The dealership is going to stop being nice to you once the main warranty expires and start messing with you to try to get you to buy another new car.
If you want to buy a used one I’d go through a broker like CarMax or Carvana, just because you can. All the organizational benefits of a dealer with none of the headaches.