We have used Garden Grocer our past few stays. As others have mentioned, their service is outstanding. In November, we were shorted the cashews we ordered. I called GG; they delivered the cashews the next morning. You can't beat that.
For our upcoming trip, I compared Garden Grocer with Instacart and Amazon Prime Now. GG had everything we wanted, but was the most expensive option. Instacart had nearly everything we need for the week PLUS it saved us about $30 over GG. Prime Now was the cheapest option, but we would have been required to purchase some fresh items from either GG or at the resort shop.
Finally, I checked the prices at the Super Target just outside of Disney property. I can get everything I need there for less than any of the aforementioned options. Now, how do I get there. Uber was only about $10 cheaper than renting a car from the Dolphin for 24 hours. Now I'll be able to get the groceries, stop by a spirits store for some rum, and grab anything else we will likely forget.
Based on my calculations, I'll still save about $35 over Garden Grocer, which is what we normally use.