Ideologically I would say the US. Morally I think most of Europe trumps the US (even though the US keeps world peace, they often breach basic human rights).
Culturally I would say Europe has the upper hand. Again this is very subjective.
Politically US is the ruler of the world, no questions asked.
If you'd just plain out ask me what's the best country in the world, out of all the ones I've been to longer than 2 weeks, it's mine. A good balance between capitalism and socialism, proud of being a once very tolerant nation, very level-headed people. With most people it'll be the country they were brought up in.