Postdoc position: should I stay for one year or two years?
Two.

In the United States, at least in computer science, most postdocs are synchronized with the academic calendar.  A typical postdoc starts in August, and faculty application deadlines start in November.  So for purposes of applying for faculty positions, a one-year postdoc is really only three months long.  A two-year postdoc gives you five times as much time to strengthen your faculty application!