Since coming back from CERN last month, this is one question I have been asked too many times - and like every other "important" question I face, this one has no clear answer. And the choice is not mine anyway. I will probably land up wherever people are kind enough to offer me to work with them. Just for argument's sake though, here are my thoughts.
The short answer would be Europe is scenic, but US feels like home. I do not know whether this is what four years of America did to me, but that is exactly how I felt after coming back. May be its the language. Or just the familiarity with everything so weirdly American. Probably a combination of both.
In Europe, I was a tourist. Everything felt alien to me. And as a tourist, that is precisely what you want. US is mostly predictable for me now - even when I go to someplace totally new here, I pretty much know what to expect, and the overall scheme of things. Exploring a new culture is definitely a learning experience, but to be a part of it may be a little too demanding. Funnily, I have heard people presenting the same argument while moving back to India from here, and I now get the point. Familiarity does not always breed contempt.
Growing up in India, where aping 70's US culture was the coolest thing for the teenagers, and now eating at MacDonald's is the idea of a family dinner, and then coming straight to US, I never saw a worldview where US is so insignificant, people are so nonchalant about USA, as I saw in Europe. And that was a welcome change. In India, we go overboard to cater to the needs of the American tourists, and at a very superficial level. The first class coach in the intercity express from Agra to Jaipur had 110 volts American plug points only. While that was helpful for me, I still think its a disgrace. In Europe, there are hoards of America tourists everywhere, but none really cares, and they struggle to find their way around, like everyone else. Of course people are in general helpful, but that's true in general, not like in Rajasthan, where "Foreign" tourists were always given a warmer reception, to put it mildly.
While these things are what I liked about Europe, precisely these make the idea of staying long term there a bit uncomfortable. The center of gravity of world science has not yet shifted back to Europe, consequently getting a job is still easier in USA. And the general perception in the community mirrors the old saying - out of sight is out of mind - it is easier to get American jobs ( "jobs" in the very broad sense of the term, anything from a post doctoral position to an appointment in a research lab, or even in industry) if one applies from US.
Academically, CERN presents an incredible opportunity roughly at at the same time when I think I would graduate. The much anticipated LHC, world's highest energy particle collider starts taking data, and for anyone in the field, that is the time to be there. However, since I am an absolute non expert of hardware, and pretty much what I need to do can be done remotely, there is no acute need for me to be there physically, although people do that all the time.
So I guess the ideal "job" would be one where I would be still based in US, but would get to travel to CERN often. The best of both worlds.
P. S - I must acknowledge one of my "blogger friends", for suggesting that I come up with a post on this.