The DJI Store, Amazon, and B&H are all great options (I shop at all often). As for the best store? Perhaps the one that has the item in stock and can deliver it the fastest.

Understanding the Context

While you probably won't have to return your drone, Amazon and B&H are likely better for returns. And if you're near a Best Buy (might have limited stock in the store), that's a great option too since you can return in person.