The question is, best in which respects? The actual land under our feet? Our original political structure? The culture? The diversity? The economic climate? The crime rates? Our universities and research environment?
I've done some traveling, too. While other countries have aspects to their culture that might be better, my overall conclusion was "I'm (very) American, and you know what? That's okay. I'm not going to apologize for it." Bringing up a few generalities:
We may be a bit workaholic, but don't underestimate the importance of a work ethic.
I hope we never lose our ethic of self-reliance. Trimming it back a wee bit might be healthy, but I still like it.
Europe may have better work/life balance, but anecdotally it is harder to break into the regular, full time workforce.
We may be facing a growing problem with income inequality, but around here, customers dressed as working class/casual/tradesmen do, on average, get a higher level of respect by default than they do in other countries. In other countries, clothes make the man/woman because you will get absolutely no help/respect if you appear to be a plebe.
We may have some ethnic/racial tensions but other countries laugh at our "problems"
Food here is still relatively cheap and high quality (I fear the latter may be on the wane, if you buy it in the normal supply chain...)
There's still plenty of places with a low cost of living and decent quality of life. Housing is way cheaper.
We have some awesome universities (and some that should be plowed under, I admit). On the average we have much less of a culture of cheating than some other places I could name.
You can travel hundreds, even thousands of miles and you are still in the same country and people are speaking the same language. We mostly take that boon for granted.
Ours on the whole is still a very open and friendly culture- to the extent that we weird out a little people from other countries.
The land itself has many beautiful places to see and gobs of resources.
Would I like to see an actual maternity leave program? Hell yes. Am I concerned about waning social mobility? Yes. Could we do better on allowing alternate transportation options to the car? Somewhat. Do I think for a second that there will be a social safety net by the time I reach old age? Not likely. And our taxation system is waaaay overdue for an overhaul.
Regardless, we have it sweeter than we sometimes realize. I find quite a few Americans who think they sounds educated and worldly by ragging on their own country and idolizing certain other locales...have never been out of the country more than two weeks.
Cultural differences can be a hard thing to wrap your mind around. What works best for Country A will not work so well with Country B. But some in Country A think Country B's differences are due to circumstance and if they could emulate the ways of Country A, they would. They just can't because of their circumstances, and we'll just be understanding of that. Then they visit Country B, talk with people there, and the residents of Country B say "Why the hell would we do it like that? Are you mad?!"
Yaaay, culture shock.