Great question. I use a similar question on my first day of my Intro to Philosophy class to help my students see that not all questions have either objective answers or subjective answers. (I use "What is the greatest rock band of all time?" to make the point.) Objectively answerable questions are ones for which we have agreed-upon methods for finding a single correct answer: Is earth bigger than mars? How many humans are in this room? What is the capital of Nigeria? ... even if we don't yet know the answer: How many planets in the Milky Way have water on them? What will I weigh at noon on Jan 21, 2012?
Subjectively answerable questions are ones that depend only on the opinion of the person answering the question: What's your favorite color? What is your favorite rock band? What is your favorite soccer team?
But what about: What is the best rock band of all time? What is the best national soccer team in the world right now? (or: Why does Hamlet wait so long to avenge his father? What led to World War II?) These questions do not seem to be objective, nor subjective. I call them normatively answerable. By that, I just mean that we have norms about what counts as better and worse answers and also norms about what counts as better and worse ways or methods of answering them, though these methods may not point to a single correct answer. We also expect people to offer justifications for their answers to these questions and we make judgments about whether their justifications are defensible, irrelevant, etc.
The Beatles and Rolling Stones are defensible answers. Back Street Boys and In Sync are not. (Of course, the best answer is Led Zeppelin, which I can defend some other time.) Spain is a very defensible answer to what is the best soccer team. Alas, the USA is not. We could provide justifications both for the specific answer and for the methods we use to obtain it.
Here's a defensible method: The reigning champion of the World Cup is the best national team (especially if it is also the reigning European champion). So, Spain. But there are other defensible methods, including ones that use statistics (win/loss/tie ration, possession percentage, goals for/against, etc.). Without looking them up, I'd guess Spain is best on just about any of these measures. So, at this point the answer to this question may be easier than at other times.
Note that if the relevant community comes to complete agreement about how to answer a question, it looks objective. What is the best movie of the year? If we all agree it's the winner of the Oscar, then the answer is objective. But typically, we have lively debates about what methods are best to answer such questions, so they remain 'normatively answerable.' (I think most, if not all, ethical questions are normatively answerable.)
I hope this helps. And I hope that someday the US might be the best answer to the soccer question, but it might take a while.