Coke is usually said to be in a glass (even if the container is not made of glass) and not a cup. Make that change and both are fine.

I agree with Oliver and Susanne. I'm in the Midwest of the USA. Note: some people use Coke as a generic name to mean any soft drink. And there are regional differences in naming a soft drink. Soda, Soda pop, pop, soft drink and cola all mean the same thing. Note#2 cups are for tea and coffee. Glasses are for all other drinks.

I would always go with the first when ordering at a restaurant.