In my experience the one in Spain is less sweet than the one in the USA. Same in France.

I recently travelled to France and the fridge was so cold it had frozen half of the coke. Then I tasted it and it felt like the USA version. But then I realized it was because most of the water was still frozen while the rest of the Coke was already getting unfrozen and felt more concentrated/sweet. For a day I thought the Coke in France was also sweeter.