I hate all the instant hot chocolate stuff you make with water. There is no point in a hot chocolate made mostly of water, it's just... wrong.
My favourite hot chocolate is either Green and Black's, or made with Drinking Chocolate Drops from a chocolate shop in my local town.
Out of the house, John Lewis/M&S hot chocolates are always a good place to start... especially in John Lewis with a pancake on the side... om nom nom.