This seems to be a pretty big debate when students are considering studying abroad. While you may think a year seems like a long time to be abroad, a semester or summer term can be too short. In addition, most universities in Europe don't begin the school year until late September, affording you only three months to get acclimated, travel, and still get your work done before you're heading back home.
I found that the longer I was abroad, the greater the academic, cultural and personal benefits I gained. By living in another country for nine to ten months as opposed to three or four, I believe you will become more involved in the local scene and get a better feel for the knowledge of the culture.
Read more: http://www.studyabroad.com/student-guide/semester-or-year.aspx#ixzz2kguFBRAQ