I use Costco's Kirkland batteries for my non-rechargeable batteries. They cost less then Duracells, and they last just as long. Though now that I think about it, my D size batteries are all Duracells, so I don't think Costco makes a D size battery.
Where are your flashlights normally stored? The reason I ask is because I use lithium batteries for the flashlights I keep in the car. Although they cost more, they last longer than standard batteries, and can handle high heat and low colds better than standard batteries. They're like the synthetic oil of batteries. All my cars have a D size maglite, and AA LED flashlights in them. The AA lights all have lithium batteries in them, because in the event I need a flashlight on the side of the road, I want to know the batteries are good and the light's going to work.