Of the three offered brands, I think I would go with Hershey's as it is an iconic American brand.
Who knows, perhaps someday your grandson will be taking his children to Hershey Park and fondly recalling how he and his grandfather used to drink the very same stuff on their hikes.
Then there is Bosco, a slightly less famous American brand. In this vision of the future, perhaps your grandson will be showing his children Hitchcock's movie Psycho and as the blood drips down the drain, he can declare, "See that stuff, it isn't blood it's really Bosco, my demented grandfather used to make me drink it all the time!"
The third vision of the future is very cloudy, but involves your grandson claiming to his incredulous children, "Really, America used to be a rich nation and made all kinds of things until the people started buying everything from foreign corporations..."
Well, I have taken off my swami hat, but I do think it is funny how seemingly inconsequential decisions can play out over time.
Disclaimer: I have a very poor track record as a swami, but I do like to wear my swami hat. I am sure in the end, what your grandson will remember are those glorious walks with his grandfather and not remember the hot chocolate at all.