My experience is a little less worldly. I live in the US, and I've visited Canada, Japan, and touristy parts of Mexico and the Carribean.
My experience is that the US, in general, came in last or tied with Mexico and the Carribean. I'm not talking bad service, just not as nice as Canada (second place) or Japan (first place).
Canadians tend to just be nice people (I've got relatives there, so I'm probably biased) and I think that's why it's got good service.
Japan has a culture of customer service that leads it to be the best, IMO. Anyone who has learned some Japanese and then visited Japan will have stories to tell you of how amazingly nice the clerks are and some of the odd situations you can get in because you don't know the culture. For instance: You aren't supposed to ask, "Do you have any (X)?" This is because they can't tell a customer "no". If you do this, they'll take you to the part of the store that would have the product, and then say something like, "It would be here if we had it."
Instead, you're supposed to say, "Do you not have (X)?" and then they can answer "Yes, we have none."
That isn't to say that people don't have bad experiences there. A co-worker of mine said she had a bad experience and found that clerks were rude to her. (She's very nice, so it wasn't her attitude or anything.) But in general, the stories I hear are of amazing levels of service.