I'm more of a traditionalist when it comes to my hot chocolate and don't like all of "add-ons" - flavorings, marshmallows, etc., although I will take some schlag on top. Therefore, my favorites:

Cafe Schober - Zurich

Weber & Weiss - Friedrichshafen, Germany

And, if you want to consider a powder that you can buy in a grocery, then, I'll take Caotina Noir. I always stock up when I'm in Switzerland or Germany.