Is it better to go for a postdoc in the US or Europe?
The answer to this question will come down to your personal circumstances and goals. There will be advantages and disadvantages to both options (both professionally and personally) that only you can know and weigh up. And, of course, it matters more how good the postdoc will be for your development than what continent it is in.

However, it sounds like your goal is to eventually end up in the US. In that case, my suggestion would be that there is no time like the present to make the move. Getting a position in the US is tough and it helps to have as many local contacts as possible, so you should start building them up as soon as possible.