What are the advantages and disadvantages of doing a postdoc in France and UK/USA? I am concluding my Ph.D. in the UK, and currently I have two postdoc offers one from the US and one from France. I am not a British/EU citizen and would like to take on an academic path preferably in an English speaking institute. Both projects that I managed to get a postdoc offer for are very interesting, and the PI's are well-known academic in the field.

Given that becoming an academic in France requires fluency in French, I was wondering what would be a wise choice here? What are the general qualities that are important for a lectureship position? I am under the impression that for STEM fields, USA is a no brainer, but acquiring a visa might be difficult for me!

Any advice is really appreciated.
I would say prestige-wise, the actual supervisor is more important than the location: A well known supervisor in France will be just as good for you as a well known supervisor in the US, there are just more of them in the US. Of course, you'd choose an unknown at Princeton over an unknown in Grenoble, but you said both are well known.  And all this only works if you are trying to stay in the same field when you move on, if you want to move on then prestige of institutions counts more. 

Research in the US is likely to be better funded than in France, and you'll likely have more chance to interact with other top researchers other than people in your own group. 

There will be far more opportunity for faculty positions, long-term, in the states than in France.

On the flip side, employment conditions will be better in France: max working times and compulsory breaks are observed: everyone takes a proper lunch and is home in time for tea, and it would be almost impossible to sack you. For the breaks and work/life balance, its is possible find this in the US, but you have to be selective about the culture of the group you join. Unfortunately no amount of selectivity can mean that the boss can't just sack you if they don't like you in the US.