In my opinion, the best way to make it at home is to buy a high-quality powder, boil water, and then add the two together. Which brands have you tried that didn't taste the same? Also, are you comparing a sugar-laden convenience store drink with a sugar-free, healthier version from the grocery store? If that's the case, it's like comparing apples to oranges -- the sugar free kind will almost always taste a little "off" as compared with the sugar-laden one. Last, if you make it at home, make sure you actually boil the water as opposed to just heating it in the microwave. One of the things about those machines in the convenience store is that they get the water REALLY hot before mixing it with the powder when you hit the button on the machine. It might sound trivial, but it really does make a difference in how the drink tastes.